Radium-223 in women with hormone receptor-positive bone-metastatic breast cancer receiving endocrine therapy: pooled analysis of two international, phase 2, randomized, double-blind, placebo-controlled trials

BACKGROUND

Most women with advanced breast cancer have skeletal metastases. Radium-223 is an alpha-emitting radionuclide that selectively targets areas of bone metastases.

METHODS

Two double-blind, placebo-controlled studies of radium-223 were conducted in women with hormone receptor-positive (HR+), bone-predominant metastatic breast cancer. All patients received endocrine therapy (ET), as a single agent of the investigator's choice (Study A) or exemestane + everolimus (Study B). Patients were randomized to receive radium-223 (55 kBq/kg) or placebo intravenously every 4 weeks for six doses. Accrual was halted following unblinded interim analyses per protocol amendments, and both studies were terminated. We report pooled analyses of symptomatic skeletal event-free survival (SSE-FS; primary endpoint), radiologic progression-free survival (rPFS) and overall survival (OS; secondary), and time to bone alkaline phosphatase (ALP) progression (exploratory).

RESULTS

In total, 382 patients were enrolled, and 196 SSE-FS events (70% planned total) were recorded. Hazard ratios (95% confidence intervals) and nominal p values for radium-223 + ET versus placebo + ET were: SSE-FS 0.809 (0.610-1.072), p = 0.1389; rPFS 0.956 (0.759-1.205), p = 0.7039; OS 0.889 (0.660-1.199), p = 0.4410; and time to bone ALP progression 0.593 (0.379-0.926), p = 0.0195. Radium-223- or placebo-related treatment-emergent adverse events were reported in 50.3% versus 35.1% of patients (grade 3/4: 25.7% vs. 8.5%), with fractures/bone-associated events in 23.5% versus 23.9%.

CONCLUSIONS

In patients with HR+ bone-metastatic breast cancer, numeric differences favoring radium-223 + ET over placebo + ET for the primary SSE-FS endpoint were suggestive of efficacy, in line with the primary outcome measure used in the underlying phase 2 studies. No similar evidence of efficacy was observed for secondary progression or survival endpoints. Adverse events were more frequent with radium-223 + ET versus placebo + ET, but the safety profile of the combination was consistent with the safety profiles of the component drugs. Clinical trial registration numbers Study A: NCT02258464, registered October 7, 2014. Study B: NCT02258451, registered October 7, 2014.

Serum methylmalonic acid concentrations at breast cancer diagnosis significantly correlate with clinical frailty

Methylmalonic acid (MMA), a by-product of propionate metabolism, is known to increase with age. This study investigates the potential of serum MMA concentrations as a biomarker for age-related clinical frailty in older patients with breast cancer. One hundred nineteen patients ≥ 70 years old with early-stage breast cancer were included (median age 76 years). G8 screening, full geriatric assessment, clinical parameters (i.e., estimated glomerular filtration rate (eGFR) and body mass index (BMI)), and serum sample collection were collected at breast cancer diagnosis before any therapy was administered. MMA concentrations were measured via liquid chromatography with tandem mass spectrometry. MMA concentrations significantly increased with age and eGFR (all P < 0.001) in this older population. The group with an abnormal G8 (≤ 14, 51% of patients) had significantly higher MMA levels than the group with normal G8 (> 14, 49%): 260 nmol/L vs. 188 nmol/L, respectively (P = 0.0004), even after correcting for age and eGFR (P = 0.001). Furthermore, in the detailed assessment, MMA concentrations correlated most with mobility (Eastern Cooperative Oncology Group (ECOG) Performance Status and Activities of Daily Living (ADL) tools, all P ≤ 0.02), comorbidity (Charlson Comorbidity Index (CCI) tool, P = 0.005), and polypharmacy (P < 0.001), whereas no significant associations were noted for instrumental ADL (IADL), Mini-Mental State Examination (MMSE), Geriatric Depression Scale-15 (GDS15), Mini Nutritional Assessment-Short Form (MNA-SF), and pain (all P > 0.1). In addition, our results showed that higher MMA levels correlate with poor overall survival in breast cancer patients (P = 0.003). Elevated serum MMA concentrations at initial diagnosis are significantly associated, not only with age but also independently with clinical frailty, suggesting a possible influence of MMA on clinical frailty in older patients with early-stage breast cancer.

Reporting on invasive lobular breast cancer in clinical trials: a systematic review

Invasive lobular breast cancer (ILC) differs from invasive breast cancer of no special type in many ways. Evidence on treatment efficacy for ILC is, however, lacking. We studied the degree of documentation and representation of ILC in phase III/IV clinical trials for novel breast cancer treatments. Trials were identified on Pubmed and clinicaltrials.gov. Inclusion/exclusion criteria were reviewed for requirements on histological subtype and tumor measurability. Documentation of ILC was assessed and ILC inclusion rate, central pathology and subgroup analyses were evaluated. Inclusion restrictions concerning tumor measurability were found in 39/93 manuscripts. Inclusion rates for ILC were documented in 13/93 manuscripts and varied between 2.0 and 26.0%. No central pathology for ILC was reported and 3/13 manuscripts had ILC sub-analyses. ILC is largely disregarded in most trials with poor representation and documentation. The current inclusion criteria using RECIST v1.1, fall short in recognizing the unique non-measurable metastatic infiltration of ILC.

Adjuvant Abemaciclib Plus Endocrine Therapy for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative, High-Risk Early Breast Cancer: Results From a Preplanned monarchE Overall Survival Interim Analysis, Including 5-Year Efficacy Outcomes

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical trial updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.Two years of adjuvant abemaciclib combined with endocrine therapy (ET) resulted in a significant improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) that persisted beyond the 2-year treatment period in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, high-risk early breast cancer (EBC). Here, we report 5-year efficacy results from a prespecified overall survival (OS) interim analysis. In the intent-to-treat population, with a median follow-up of 54 months, the benefit of abemaciclib was sustained with hazard ratios of 0.680 (95% CI, 0.599 to 0.772) for IDFS and 0.675 (95% CI, 0.588 to 0.774) for DRFS. This persistence of abemaciclib benefit translated to continuous separation of the curves with a deepening in 5-year absolute improvement in IDFS and DRFS rates of 7.6% and 6.7%, respectively, compared with rates of 6% and 5.3% at 4 years and 4.8% and 4.1% at 3 years. With fewer deaths in the abemaciclib plus ET arm compared with the ET-alone arm (208 v 234), statistical significance was not reached for OS. No new safety signals were observed. In conclusion, abemaciclib plus ET continued to reduce the risk of developing invasive and distant disease recurrence beyond the completion of treatment. The increasing absolute improvement at 5 years is consistent with a carryover effect and further supports the use of abemaciclib in patients with high-risk EBC.

Nonlinear Mixed-Effects Model of Z-Endoxifen Concentrations in Tamoxifen-Treated Patients from the CEPAM Cohort

Tamoxifen is widely used in patients with hormone receptor-positive breast cancer. The polymorphic enzyme CYP2D6 is primarily responsible for metabolic activation of tamoxifen, resulting in substantial interindividual variability of plasma concentrations of its most important metabolite, Z-endoxifen. The Z-endoxifen concentration thresholds below which tamoxifen treatment is less efficacious have been proposed but not validated, and prospective trials of individualized tamoxifen treatment to achieve Z-endoxifen concentration thresholds are considered infeasible. Therefore, we aim to validate the association between Z-endoxifen concentration and tamoxifen treatment outcomes, and identify a Z-endoxifen concentration threshold of tamoxifen efficacy, using pharmacometric modeling and simulation. As a first step, the CYP2D6 Endoxifen Percentage Activity Model (CEPAM) cohort was created by pooling data from 28 clinical studies (> 7,000 patients) with measured endoxifen plasma concentrations. After cleaning, data from 6,083 patients were used to develop a nonlinear mixed-effect (NLME) model for tamoxifen and Z-endoxifen pharmacokinetics that includes a conversion factor to allow inclusion of studies that measured total endoxifen but not Z-endoxifen. The final parent-metabolite NLME model confirmed the primary role of CYP2D6, and contributions from body weight, CYP2C9 phenotype, and co-medication with CYP2D6 inhibitors, on Z-endoxifen pharmacokinetics. Future work will use the model to simulate Z-endoxifen concentrations in patients receiving single agent tamoxifen treatment within large prospective clinical trials with long-term survival to identify the Z-endoxifen concentration threshold below which tamoxifen is less efficacious. Identification of this concentration threshold would allow personalized tamoxifen treatment to improve outcomes in patients with hormone receptor-positive breast cancer.

Aging-accumulated methylmalonic acid serum levels at breast cancer diagnosis are not associated with distant metastases

PURPOSE

Recent evidence suggests that age-accumulated methylmalonic acid (MMA) promotes breast cancer progression in mice. This study aims to investigate the association between baseline serum MMA concentrations in patients with breast cancer and the development of subsequent distant metastases.

METHODS

We included 32 patients with early Luminal B-like breast cancer (LumB, median age 62.4y) and 52 patients with early triple-negative breast cancer (TNBC, median age 50.5y) who developed distant metastases within 5 years. They were matched to an equal number of early breast cancer patients (median age 62.2y for LumB and 50.5y for TNBC) who did not develop distant metastases with at least 5 years of follow-up.

RESULTS

Baseline serum MMA levels at breast cancer diagnosis showed a positive correlation with age (P < 0.001) and a negative correlation with renal function and vitamin B12 (all P < 0.02), but no statistical association was found with BMI or tumor stage (P > 0.6). Between matched pairs, no significant difference was observed in MMA levels, after adjusting for kidney function and age (P = 0.19). Additionally, in a mouse model, a significant decline in MMA levels was observed in the tumor-bearing group compared to the group without tumors before and after tumor establishment or at identical times for the control group (P = 0.03).

CONCLUSION

Baseline serum MMA levels in patients with breast cancer are not correlated with secondary distant metastasis. Evidence in the mouse model suggests that the presence of a tumor perturbates MMA levels.

Treatment Response, Tumor Infiltrating Lymphocytes and Clinical Outcomes in Inflammatory Breast Cancer-Treated with Neoadjuvant Systemic Therapy

Inflammatory breast cancer (IBC) is a rare (1%-5%), aggressive form of breast cancer, accounting for approximately 10% of breast cancer mortality. In the localized setting, standard of care is neoadjuvant chemotherapy (NACT) ± anti-HER2 therapy, followed by surgery. Here we investigated associations between clinicopathologic variables, stromal tumor-infiltrating lymphocytes (sTIL), and pathologic complete response (pCR), and the prognostic value of pCR. We included 494 localized patients with IBC treated with NACT from October 1996 to October 2021 in eight European hospitals. Standard clinicopathologic variables were collected and central pathologic review was performed, including sTIL. Associations were assessed using Firth logistic regression models. Cox regressions were used to evaluate the role of pCR and residual cancer burden (RCB) on disease-free survival (DFS), distant recurrence-free survival (DRFS), and overall survival (OS). Distribution according to receptor status was as follows: 26.4% estrogen receptor negative (ER-)/HER2-; 22.0% ER-/HER2+; 37.4% ER+/HER2-, and 14.1% ER+/HER2+. Overall pCR rate was 26.3%, being highest in the HER2+ groups (45.9% for ER-/HER2+ and 42.9% for ER+/HER2+). sTILs were low (median: 5.3%), being highest in the ER-/HER2- group (median: 10%). High tumor grade, ER negativity, HER2 positivity, higher sTILs, and taxane-based NACT were significantly associated with pCR. pCR was associated with improved DFS, DRFS, and OS in multivariable analyses. RCB score in patients not achieving pCR was independently associated with survival. In conclusion, sTILs were low in IBC, but were predictive of pCR. Both pCR and RCB have an independent prognostic role in IBC treated with NACT.

SIGNIFICANCE

IBC is a rare, but very aggressive type of breast cancer. The prognostic role of pCR after systemic therapy and the predictive value of sTILs for pCR are well established in the general breast cancer population; however, only limited information is available in IBC. We assembled the largest retrospective IBC series so far and demonstrated that sTIL is predictive of pCR. We emphasize that reaching pCR remains of utmost importance in IBC.

AMEERA-4: a randomized, preoperative window-of-opportunity study of amcenestrant versus letrozole in early breast cancer

BACKGROUND

Window-of-opportunity (WOO) studies provide insights into the clinical activity of new drugs in breast cancer.

METHODS

AMEERA-4 (NCT04191382) was a WOO study undertaken to compare the pharmacodynamic effects of amcenestrant, a selective estrogen receptor degrader, with those of letrozole in postmenopausal women with newly diagnosed, operable estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer. Women were randomized (1:1:1) to receive amcenestrant 400 mg, amcenestrant 200 mg, or letrozole 2.5 mg once daily for 14 days before breast surgery. The primary endpoint was change in Ki67 between baseline and Day 15 (i.e., day of surgery).

RESULTS

Enrollment was stopped early because of slow recruitment, in the context of the COVID-19 pandemic. The modified intent-to-treat population consisted of 95 study participants with baseline and post-treatment Ki67 values, whereas the safety population included 104 participants who had received at least one dose of study medication. Relative change from baseline in Ki67 was - 75.9% (95% confidence interval [CI] - 81.9 to - 67.9) for amcenestrant 400 mg, - 68.2% (- 75.7 to - 58.4) for amcenestrant 200 mg, and - 77.7% (- 83.4 to - 70.0) for letrozole (geometric least-squares mean [LSM] estimates). Absolute change in ER H-score from baseline (LSM estimate) was - 176.7 in the amcenestrant 400 mg arm, - 202.9 in the amcenestrant 200 mg arm, and - 32.5 in the letrozole arm. There were no Grade ≥ 3 treatment-related adverse events.

CONCLUSIONS

Both amcenestrant and letrozole demonstrated antiproliferative activity in postmenopausal women with previously untreated, operable ER+/HER2- breast cancer and had good overall tolerability.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04191382 https://clinicaltrials.gov/ct2/show/NCT04191382 . Registered 9 December 2019.

The effect of myofascial and physical therapy on trunk, shoulder, and elbow movement patterns in women with pain and myofascial dysfunctions after breast cancer surgery: Secondary analyses of a randomized controlled trial

INTRODUCTION

Secondary upper limb dysfunctions are common after breast cancer treatment. Myofascial treatment may be a valuable physical therapy modality for this problem.

OBJECTIVE

To investigate the effect of myofascial therapy in addition to physical therapy on shoulder, trunk, and elbow movement patterns in women with pain and myofascial dysfunctions at the upper limb after breast cancer surgery.

DESIGN

A double-blinded randomized controlled trial.

SETTING

Rehabilitation unit of a university hospital.

PARTICIPANTS

Forty-eight women with persistent pain after finishing breast cancer treatment.

INTERVENTIONS

Over 3 months, all participants received a standard physical therapy program. The experimental (n = 24) and control group (n = 24) received 12 additional sessions of myofascial therapy or placebo therapy, respectively.

MAIN OUTCOME MEASURES

Outcomes of interest were movement patterns of the humerothoracic joint, scapulothoracic joint, trunk, and elbow, measured with an optoelectronic measurement system during the performance of a forward flexion and scaption task. Statistical parametric mapping (SPM) analyses were used for assessing the effect of treatment on movement patterns between both groups (group × time interaction effect).

RESULTS

A significantly decreased protraction and anterior tilting was found after experimental treatment. No beneficial effects on movement patterns of the humerothoracic joint, trunk, or elbow were found.

CONCLUSION

Myofascial therapy in addition to a 12-week standard physical therapy program can decrease scapular protraction and anterior tilting (scapulothoracic joint) during arm movements. Given the exploratory nature of these secondary analyses, the clinical relevance of these results needs to be investigated further.

Pooled ctDNA analysis of MONALEESA phase III advanced breast cancer trials

BACKGROUND

The phase III MONALEESA trials tested the efficacy and safety of the cyclin-dependent kinase (CDK)4/6 inhibitor ribociclib with different endocrine therapy partners as first- or second-line treatment of hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer (ABC). Using the largest pooled biomarker dataset of the CDK4/6 inhibitor ribociclib in ABC to date, we identified potential biomarkers of response to ribociclib.

PATIENTS AND METHODS

Baseline circulating tumour DNA from patients in the MONALEESA trials was assessed using next-generation sequencing. An analysis of correlation between gene alteration status and progression-free survival (PFS) was carried out to identify potential biomarkers of response to ribociclib.

RESULTS

Multiple frequently altered genes were identified. Alterations in ERBB2, FAT3, FRS2, MDM2, SFRP1, and ZNF217 were associated with a greater PFS benefit with ribociclib versus placebo. Patients with high tumour mutational burden (TMB) and with ANO1, CDKN2A/2B/2C, and RB1 alterations exhibited decreased sensitivity to ribociclib versus placebo.

CONCLUSIONS

Although exploratory, these results provide insight into alterations associated with the improved response to ribociclib treatment and may inform treatment sequencing in patients with actionable alterations following progression on CDK4/6 inhibitors. Validation of potential biomarkers identified here and development of prospective trials testing their clinical utility are warranted.

CLINICALTRIALS

GOV IDENTIFIERS

NCT01958021, NCT02422615, NCT02278120.

Circulating biomarkers at diagnosis correlate with distant metastases of early luminal-like breast cancer

There is an urgent need for new and better biomarker modalities to estimate the risk of recurrence within the luminal-like breast cancer (BC) population. Molecular diagnostic tests used in the clinic lack accuracy in identifying patients with early luminal BC who are likely to develop metastases. This study provides proof of concept that various liquid biopsy read-outs could serve as valuable candidates to build a multi-modal biomarker model distinguishing, already at diagnosis, between early metastasizing and non-metastasizing patients. All these blood biomarkers (chemokines, microRNAs, leukemia inhibitory factor, osteopontin, and serum-induced functional myeloid signaling responses) can be measured in baseline plasma/serum samples and could be added to the existing prognostic factors to improve risk stratification and more patient-tailored treatment in early luminal BC.

Poor Outcome in Postpartum Breast Cancer Patients Is Associated with Distinct Molecular and Immunologic Features

PURPOSE

Patients with postpartum breast cancer diagnosed after cessation of breastfeeding (postweaning, PP-BCPW) have a particularly poor prognosis compared with patients diagnosed during lactation (PP-BCDL), or to pregnant (Pr-BC) and nulliparous (NP-BC) patients, regardless of standard prognostic characteristics. Animal studies point to a role of the involution process in stimulation of tumor growth in the mammary gland. However, in women, the molecular mechanisms that underlie this poor prognosis of patients with PP-BCPW remain vastly underexplored, due to of lack of adequate patient numbers and outcome data.

EXPERIMENTAL DESIGN

We explored whether distinct prognostic features, common to all breast cancer molecular subtypes, exist in postpartum tumor tissue. Using detailed breastfeeding data, we delineated the postweaning period in PP-BC as a surrogate for mammary gland involution and performed whole transcriptome sequencing, immunohistochemical, and (multiplex) immunofluorescent analyses on tumor tissue of patients with PP-BCPW, PP-BCDL, Pr-BC, and NP-BC.

RESULTS

We found that patients with PP-BCPW having a low expression level of an immunoglobulin gene signature, but high infiltration of plasma B cells, have an increased risk for metastasis and death. Although PP-BCPW tumor tissue was also characterized by an increase in CD8+ cytotoxic T cells and reduced distance among these cell types, these parameters were not associated with differential clinical outcomes among groups.

CONCLUSIONS

These data point to the importance of plasma B cells in the postweaning mammary tumor microenvironment regarding the poor prognosis of PP-BCPW patients. Future prospective and in-depth research needs to further explore the role of B-cell immunobiology in this specific group of young patients with breast cancer.

Association of body mass index with clinicopathological features and survival in patients with primary invasive lobular breast cancer

PURPOSE

Invasive lobular carcinoma (ILC) represents up to 15% of all breast carcinomas. While the proportion of women with overweight and obesity increases globally, the impact of body mass index (BMI) at primary diagnosis on clinicopathological features of ILC and the prognosis of the patients has not been investigated yet.

PATIENTS AND METHODS

We performed a multicentric retrospective study including patients diagnosed with non-metastatic pure ILC. The association of BMI at diagnosis with clinicopathological variables was assessed using linear or multinomial logistic regression. Univariable and multivariable survival analyses were performed to evaluate the association of BMI with disease-free survival (DFS), distant recurrence-free survival (DRFS), and overall survival (OS).

RESULTS

The data of 2856 patients with ILC and available BMI at diagnosis were collected, of which 2570/2856 (90.0%) had oestrogen receptor (ER)-positive and human epidermal growth factor receptor (HER2) not amplified/overexpressed (ER+/HER2-) ILC. Of these 2570 patients, 80 were underweight (3.1%), 1410 were lean (54.9%), 712 were overweight (27.7%), and 368 were obese (14.3%). Older age at diagnosis, a higher tumour grade, a larger tumour size, a nodal involvement, and multifocality were associated with a higher BMI. In univariable models, higher BMI was associated with worse outcomes for all end-points (DFS: hazard ratio (HR) 1.21, 95CI 1.12-1.31, p value<0.01; DRFS: HR 1.25, 95CI 1.12-1.40, p value<0.01; OS: HR 1.25, 95CI 1.13-1.37, p value<0.01). This association was not statistically significant in multivariable analyses (DFS: HR 1.09, 95CI 0.99-1.20, p value 0.08; DRFS: HR 1.03, 95CI 0.89-1.20, p value 0.67; OS: HR 1.11, 95CI 0.99-1.24, p value 0.08), whereas grade, tumour size, and nodal involvement were still prognostic for all end-points.

CONCLUSION

Worse prognostic factors such as higher grade, larger tumour size, and nodal involvement are associated with higher BMI in ER+/HER2- ILC, while there was no statistical evidence for an independent prognostic role for BMI. Therefore, we hypothesise that the effect of BMI on survival could be mediated through its association with these clinicopathological variables.

Updated overall survival from the MONALEESA-3 trial in postmenopausal women with HR+/HER2- advanced breast cancer receiving first-line ribociclib plus fulvestrant

BACKGROUND

The phase III MONALEESA-3 trial included first- (1L) and second-line (2L) patients and demonstrated a significant overall survival (OS) benefit for ribociclib + fulvestrant in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC) in the final protocol-specified and exploratory (longer follow-up) OS analyses. At the time of these analyses, the full OS benefit of 1L ribociclib was not completely characterized because the median OS (mOS) was not reached. As CDK4/6 inhibitor (CDK4/6i) + endocrine therapy (ET) is now a preferred option for 1L HR+/HER2- ABC, we report an exploratory analysis (median follow-up, 70.8 months; 14.5 months longer than the prior analysis) to fully elucidate the OS benefit in the MONALEESA-3 1L population.

METHODS

Postmenopausal patients with HR+/HER2- ABC were randomized 2:1 to 1L/2L fulvestrant + ribociclib or placebo. OS in 1L patients (de novo disease or relapse > 12 months from completion of [neo]adjuvant ET) was assessed by Cox proportional hazards model and Kaplan-Meier methods. Progression-free survival 2 (PFS2) and chemotherapy-free survival (CFS) were analyzed. MONALEESA-3 is registered with ClinicalTrials.gov (NCT02422615).

RESULTS

At data cutoff (January 12, 2022; median follow-up time, 70.8 months), mOS was 67.6 versus 51.8 months with 1L ribociclib versus placebo (hazard ratio (HR) 0.67; 95% CI 0.50-0.90); 16.5% and 8.6% of ribociclib and placebo patients, respectively, were still receiving treatment. PFS2 (HR 0.64) and CFS (HR 0.62) favored ribociclib versus placebo. Among those who discontinued treatment, 16.7% and 35.0% on ribociclib or placebo, respectively, received a subsequent CDK4/6i. No new safety signals were observed.

CONCLUSIONS

This analysis of MONALEESA-3 reports the longest mOS thus far (67.6 months) for 1L patients in a phase III ABC trial. These results in a 1L population show that the OS benefit of ribociclib was maintained through extended follow-up, further supporting its use in HR+/HER2- ABC.

Differences in the Tumor Molecular and Microenvironmental Landscape between Early (Non-Metastatic) and De Novo Metastatic Primary Luminal Breast Tumors

Background: The molecular mechanisms underlying the de novo metastasis of luminal breast cancer (dnMBC) remain largely unknown. Materials and Methods: Newly diagnosed dnMBC patients (grade 2/3, ER+, PR+/-, HER2-), with available core needle biopsy (CNB), collected from the primary tumor, were selected from our clinical-pathological database. Tumors from dnMBC patients were 1:1 pairwise matched (n = 32) to tumors from newly diagnosed patients who had no distant metastases at baseline (eBC group). RNA was extracted from 5 × 10 µm sections of FFPE CNBs. RNA sequencing was performed using the Illumina platform. Differentially expressed genes (DEG)s were assessed using EdgeR; deconvolution was performed using CIBERSORTx to assess immune cell fractions. A paired Wilcoxon test was used to compare dnMBC and eBC groups and corrected for the false discovery rate. Results: Many regulatory DEGs were significantly downregulated in dnMBC compared to eBC. Also, immune-related and hypoxia-related signatures were significantly upregulated. Paired Wilcoxon analysis showed that the CCL17 and neutrophils fraction were significantly upregulated, whereas the memory B-cell fraction was significantly downregulated in the dnMBC group. Conclusions: Primary luminal tumors of dnMBC patients display significant transcriptomic and immunological differences compared to comparable tumors from eBC patients.

Association of the CHEK2 c.1100delC variant, radiotherapy, and systemic treatment with contralateral breast cancer risk and breast cancer-specific survival

BACKGROUND

Breast cancer (BC) patients with a germline CHEK2 c.1100delC variant have an increased risk of contralateral BC (CBC) and worse BC-specific survival (BCSS) compared to non-carriers.

AIM

To assessed the associations of CHEK2 c.1100delC, radiotherapy, and systemic treatment with CBC risk and BCSS.

METHODS

Analyses were based on 82,701 women diagnosed with a first primary invasive BC including 963 CHEK2 c.1100delC carriers; median follow-up was 9.1 years. Differential associations with treatment by CHEK2 c.1100delC status were tested by including interaction terms in a multivariable Cox regression model. A multi-state model was used for further insight into the relation between CHEK2 c.1100delC status, treatment, CBC risk and death.

RESULTS

There was no evidence for differential associations of therapy with CBC risk by CHEK2 c.1100delC status. The strongest association with reduced CBC risk was observed for the combination of chemotherapy and endocrine therapy [HR (95% CI): 0.66 (0.55-0.78)]. No association was observed with radiotherapy. Results from the multi-state model showed shorter BCSS for CHEK2 c.1100delC carriers versus non-carriers also after accounting for CBC occurrence [HR (95% CI): 1.30 (1.09-1.56)].

CONCLUSION

Systemic therapy was associated with reduced CBC risk irrespective of CHEK2 c.1100delC status. Moreover, CHEK2 c.1100delC carriers had shorter BCSS, which appears not to be fully explained by their CBC risk.

Obesity-associated changes in molecular biology of primary breast cancer

Obesity is associated with an increased risk of developing breast cancer (BC) and worse prognosis in BC patients, yet its impact on BC biology remains understudied in humans. This study investigates how the biology of untreated primary BC differs according to patients' body mass index (BMI) using data from >2,000 patients. We identify several genomic alterations that are differentially prevalent in overweight or obese patients compared to lean patients. We report evidence supporting an ageing accelerating effect of obesity at the genetic level. We show that BMI-associated differences in bulk transcriptomic profile are subtle, while single cell profiling allows detection of more pronounced changes in different cell compartments. These analyses further reveal an elevated and unresolved inflammation of the BC tumor microenvironment associated with obesity, with distinct characteristics contingent on the estrogen receptor status. Collectively, our analyses imply that obesity is associated with an inflammaging-like phenotype. We conclude that patient adiposity may play a significant role in the heterogeneity of BC and should be considered for BC treatment tailoring.

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors: existing and emerging differences

The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors palbociclib, ribociclib, and abemaciclib are standard-of-care therapy for hormone receptor-positive advanced or metastatic breast cancer, based on randomized trials showing improved progression-free survival for all 3 drugs and overall survival for ribociclib and abemaciclib. Results in early breast cancer are discordant, with sustained improvement in invasive disease-free survival demonstrated for abemaciclib but not other CDK4/6 inhibitors to date. We review nonclinical studies exploring mechanistic differences between the drugs, the impact of continuous dosing on treatment effect, and translational research into potential resistance mechanisms and prognostic and predictive markers. We focus particularly on how emerging findings may help us understand similarities and differences between the available CDK4/6 inhibitors. Even at late-stage clinical development, there remains much to learn about how agents in this class exert their varying effects.

Intra-patient and inter-metastasis heterogeneity of HER2-low status in metastatic breast cancer

INTRODUCTION

Anti-HER2 antibody-drug conjugates (ADCs) have shown important efficacy in HER2-low metastatic breast cancer (mBC). Criteria for receiving ADCs are based on a single assay on the primary tumour or a small metastatic biopsy. We assessed the intra-patient inter-metastasis heterogeneity of HER2-low status in HER2-negative mBC.

PATIENTS AND METHODS

We included samples of 10 patients (7 ER-positive and 3 ER-negative) donated in the context of our post-mortem tissue donation program UPTIDER. Excisional post-mortem biopsies of 257 metastases and 8 breast tumours underwent central HER2 immunohistochemistry (IHC), alongside 41 pre-mortem primary or metastatic samples. They were classified as HER2-zero, HER2-low (HER2-1+ or HER2-2+, in situ hybridisation [ISH] negative) or HER2-positive (HER2-3+ or HER2-2+, ISH-positive) following ASCO/CAP guidelines 2018. HER2-zero was further subdivided into HER2-undetected (no staining) and HER2-ultralow (faint staining in ≤10% of tumour cells).

RESULTS

Median post-mortem interval was 2.5 h. In 8/10 patients, HER2-low and HER2-zero metastases co-existed, with the proportion of HER2-low lesions ranging from 5% to 89%. A total of 32% of metastases currently classified as HER2-zero were HER2-ultralow. Intra-organ inter-metastasis heterogeneity of HER2-scores was observed in the liver in 3/6 patients. Patients with primary ER-positive disease had a higher proportion of HER2-low metastases as compared to ER-negative disease (46% versus 8%, respectively). At the metastasis level, higher percentages of ER-expressing cells were observed in HER2-low or -ultralow as compared to HER2-undetected metastases.

CONCLUSIONS

Important intra-patient inter-metastasis heterogeneity of HER2-low status exists. This questions the validity of HER2-low in its current form as a theranostic marker.

PARP inhibitor predictive value of the Leuven HRD test compared with Myriad MyChoice CDx PLUS HRD on 468 ovarian cancer patients from the PAOLA-1/ENGOT-ov25 trial

BACKGROUND

The PAOLA-1/ENGOT-ov25 trial showed improved progression-free (PFS) and overall survival (OS) in homologous recombination deficient (HRD) positive patients treated with olaparib, but not when HRD negative (HRD tested with MyChoice CDx PLUS [Myriad test]).

PATIENTS AND METHODS

The academic Leuven HRD test consists of capture-based targeted sequencing of genome-wide single-nucleotide polymorphisms and coding exons of eight HR genes including BRCA1, BRCA2, and TP53. We compared the predictive value of the Leuven HRD versus Myriad HRD test for PFS and OS in the randomised PAOLA-1 trial.

RESULTS

468 patients had left-over DNA after Myriad testing for Leuven HRD testing. Positive/negative/overall percent agreement for the Leuven versus Myriad HRD status was 95%/86%/91%, respectively. Tumours were HRD+ in 55% and 52%, respectively. In Leuven HRD+ patients, 5years PFS (5yPFS) was 48.6% versus 20.3% (HR 0.431; 95% confidence intervals (CI) 0.312-0.595) for olaparib versus placebo, respectively (Myriad test 0.409; 95% CI 0.292-0.572). In Leuven HRD+/BRCAwt patients 5yPFS was 41.3% versus 12.6% (HR 0.497; 95% CI 0.316-0.783), and 43.6% versus 13.3% (HR 0.435; 95% CI 0.261-0.727) for the Myriad test. 5yOS was prolonged in the HRD+ subgroup with both tests 67.2% versus 54.4% (HR 0.663; 95% CI 0.442-0.995) for the Leuven test, and 68.0% versus 51.8% (HR 0.596 95% CI 0.393-0.904) for the Myriad test. HRD status was undetermined in 10.7% and 9.4% of the samples, respectively.

CONCLUSIONS

A robust correlation between the Leuven HRD and Myriad test was observed. For HRD+ tumours, the academic Leuven HRD showed a similar difference in PFS and OS as the Myriad test.

XENERA-1: a randomised double-blind Phase II trial of xentuzumab in combination with everolimus and exemestane versus everolimus and exemestane in patients with hormone receptor-positive/HER2-negative metastatic breast cancer and non-visceral disease

BACKGROUND

Xentuzumab is a humanised monoclonal antibody that binds to IGF-1 and IGF-2, neutralising their proliferative activity and restoring inhibition of AKT by everolimus. This study evaluated the addition of xentuzumab to everolimus and exemestane in patients with advanced breast cancer with non-visceral disease.

METHODS

This double-blind, randomised, Phase II study was undertaken in female patients with hormone-receptor (HR)-positive/human epidermal growth factor 2 (HER2)-negative advanced breast cancer with non-visceral disease who had received prior endocrine therapy with or without CDK4/6 inhibitors. Patients received a weekly intravenous infusion of xentuzumab (1000 mg) or placebo in combination with everolimus (10 mg/day orally) and exemestane (25 mg/day orally). The primary endpoint was progression-free survival (PFS) per independent review.

RESULTS

A total of 103 patients were randomised and 101 were treated (n = 50 in the xentuzumab arm and n = 51 in the placebo arm). The trial was unblinded early due to high rates of discordance between independent and investigator assessment of PFS. Per independent assessment, median PFS was 12.7 (95% CI 6.8-29.3) months with xentuzumab and 11.0 (7.7-19.5) months with placebo (hazard ratio 1.19; 95% CI 0.55-2.59; p = 0.6534). Per investigator assessment, median PFS was 7.4 (6.8-9.7) months with xentuzumab and 9.2 (5.6-14.4) months with placebo (hazard ratio 1.23; 95% CI 0.69-2.20; p = 0.4800). Tolerability was similar between the arms, with diarrhoea (33.3-56.0%), fatigue (33.3-44.0%) and headache (21.6-40.0%) being the most common treatment-emergent adverse events. The incidence of grade ≥ 3 hyperglycaemia was similar between the xentuzumab (2.0%) and placebo (5.9%) arms.

CONCLUSIONS

While this study demonstrated that xentuzumab could be safely combined with everolimus and exemestane in patients with HR-positive/HER2-negative advanced breast cancer with non-visceral disease, there was no PFS benefit with the addition of xentuzumab. Trial registration ClinicalTrials.gov, NCT03659136. Prospectively registered, September 6, 2018.

Machine Learning Algorithm to Estimate Distant Breast Cancer Recurrence at the Population Level with Administrative Data

Purpose

High-quality population-based cancer recurrence data are scarcely available, mainly due to complexity and cost of registration. For the first time in Belgium, we developed a tool to estimate distant recurrence after a breast cancer diagnosis at the population level, based on real-world cancer registration and administrative data.

Methods

Data on distant cancer recurrence (including progression) from patients diagnosed with breast cancer between 2009-2014 were collected from medical files at 9 Belgian centers to train, test and externally validate an algorithm (i.e., gold standard). Distant recurrence was defined as the occurrence of distant metastases between 120 days and within 10 years after the primary diagnosis, with follow-up until December 31, 2018. Data from the gold standard were linked to population-based data from the Belgian Cancer Registry (BCR) and administrative data sources. Potential features to detect recurrences in administrative data were defined based on expert opinion from breast oncologists, and subsequently selected using bootstrap aggregation. Based on the selected features, classification and regression tree (CART) analysis was performed to construct an algorithm for classifying patients as having a distant recurrence or not.

Results

A total of 2507 patients were included of whom 216 had a distant recurrence in the clinical data set. The performance of the algorithm showed sensitivity of 79.5% (95% CI 68.8-87.8%), positive predictive value (PPV) of 79.5% (95% CI 68.8-87.8%), and accuracy of 96.7% (95% CI 95.4-97.7%). The external validation resulted in a sensitivity of 84.1% (95% CI 74.4-91.3%), PPV of 84.1% (95% CI 74.4-91.3%), and an accuracy of 96.8% (95% CI 95.4-97.9%).

Conclusion

Our algorithm detected distant breast cancer recurrences with an overall good accuracy of 96.8% for patients with breast cancer, as observed in the first multi-centric external validation exercise.

Bowel obstruction in advanced tubo-ovarian cancer: a retrospective cohort study

Ten to fifty percent of women with advanced or recurrent ovarian cancer develop malignant bowel obstruction (MBO). We described the management and examined the complications and survival of MBO in primary epithelial tubo-ovarian cancer patients.

Materials and methods

The authors conducted a retrospective monocentric cohort study of tubo-ovarian cancer patients diagnosed with MBO between January 1st, 2011 until August 31st, 2017 at the University Hospitals Leuven, Belgium.

Results

Seventy-three patients with a total of 165 MBO episodes (median 1/patient; range 1-14) were included. The median time interval between cancer diagnosis and first MBO episode was 373 days (range 0-1937). The median time interval between MBO episodes was 44 days (range 6-2004). Complications were bowel perforation (n=5; 7%) and bowel ischemia (n=1; 1%). Conservative treatment was applied in 150 (91%) episodes, including gastrostomy in 4 (2%) episodes and octreotide in 79 (48%) episodes. Surgery was necessary in 15 (9%) episodes. Total parenteral nutrition was administered in 16 (22%) patients. During the study period 62 (85%) patients died (median 167 days since first MBO; range 6-2256). A significant difference in survival was found regarding the tumor marker CA 125 at cancer diagnosis, the use of palliative chemotherapy after the first episode of MBO and palliative surgical treatment for MBO in a group of well selected patients.

Conclusion

Tubo-ovarian cancer patients with MBO have a poor prognosis: 85% of the study population died within a relatively short time interval since the first MBO. In our study population, the majority of patients with MBO were treated conservatively. Both palliative chemotherapy and palliative surgical management are considerable treatment options depending on the individual patient profile.

Mortality and Major Adverse Cardiac Events in Patients With Breast Cancer Receiving Radiotherapy: The First Decade

Background Treatment for breast cancer (BC) frequently involves radiotherapy. Guidelines recommend screening for cardiac adverse events starting 10 years after radiotherapy. The rationale for this interval is unclear. Methods and Results We aimed to study cardiovascular event rates in the first decade following curative radiotherapy for BC. We compared mortality and cardiovascular event rates with an age- and risk factor-matched control population. We included 1095 patients with BC (mean age 56±12 years). Two hundred and eighteen (19.9%) women died. Cancer and cardiovascular mortality caused 107 (49.1%) and 22 (10.1%) deaths, respectively. A total of 904 cases were matched to female FLEMENGHO (Flemish Study on Environment, Genes and Health Outcomes) participants. Coronary artery disease incidence was similar (risk ratio [RR], 0.75 [95% CI, 0.48-1.18]), yet heart failure (RR, 1.97 [95% CI, 1.19-3.25]) and atrial fibrillation/flutter (RR, 1.82 [95% CI, 1.07-3.08]) occurred more often in patients with BC. Age (hazard ratio [HR], 1.033 [95% CI, 1.006-1.061], P=0.016), tumor grade (HR, 1.739 [95% CI, 1.166-2.591], P=0.007), and neoadjuvant treatment setting (HR, 2.782 [95% CI, 1.304-5.936], P=0.008) were risk factors for mortality. Risk factors for major adverse cardiac events were age (HR, 1.053 [95% CI, 1.013-1.093]; P=0.008), mean heart dose (HR, 1.093 [95% CI, 1.025-1.167]; P=0.007), history of cardiovascular disease (HR, 2.386 [95% CI, 1.096-6.197]; P=0.029) and Mayo Clinic Cardiotoxicity Risk Score (HR, 2.664 [95% CI, 1.625-4.367]; P<0.001). Conclusions Ten-year mortality following curative treatment for unilateral BC was mainly cancer related, but heart failure and atrial fibrillation/flutter were already common in the first decade following irradiation. Mean heart dose, pre-existing cardiovascular diseases, and Mayo Clinic Cardiotoxicity Risk Score were risk factors for cardiac adverse events. These results suggest a need for early dedicated cardio-oncological follow-up after radiotherapy.

Genomic characterisation of hormone receptor-positive breast cancer arising in very young women

BACKGROUND

Very young premenopausal women diagnosed with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+HER2-) early breast cancer (EBC) have higher rates of recurrence and death for reasons that remain largely unexplained.

PATIENTS AND METHODS

Genomic sequencing was applied to HR+HER2- tumours from patients enrolled in the Suppression of Ovarian Function Trial (SOFT) to determine genomic drivers that are enriched in young premenopausal women. Genomic alterations were characterised using next-generation sequencing from a subset of 1276 patients (deep targeted sequencing, n = 1258; whole-exome sequencing in a young-age, case-control subsample, n = 82). We defined copy number (CN) subgroups and assessed for features suggestive of homologous recombination deficiency (HRD). Genomic alteration frequencies were compared between young premenopausal women (<40 years) and older premenopausal women (≥40 years), and assessed for associations with distant recurrence-free interval (DRFI) and overall survival (OS).

RESULTS

Younger women (<40 years, n = 359) compared with older women (≥40 years, n = 917) had significantly higher frequencies of mutations in GATA3 (19% versus 16%) and CN amplifications (CNAs) (47% versus 26%), but significantly lower frequencies of mutations in PIK3CA (32% versus 47%), CDH1 (3% versus 9%), and MAP3K1 (7% versus 12%). Additionally, they had significantly higher frequencies of features suggestive of HRD (27% versus 21%) and a higher proportion of PIK3CA mutations with concurrent CNAs (23% versus 11%). Genomic features suggestive of HRD, PIK3CA mutations with CNAs, and CNAs were associated with significantly worse DRFI and OS compared with those without these features. These poor prognostic features were enriched in younger patients: present in 72% of patients aged <35 years, 54% aged 35-39 years, and 40% aged ≥40 years. Poor prognostic features [n = 584 (46%)] versus none [n = 692 (54%)] had an 8-year DRFI of 84% versus 94% and OS of 88% versus 96%. Younger women (<40 years) had the poorest outcomes: 8-year DRFI 74% versus 85% and OS 80% versus 93%, respectively.

CONCLUSION

These results provide insights into genomic alterations that are enriched in young women with HR+HER2- EBC, provide rationale for genomic subgrouping, and highlight priority molecular targets for future clinical trials.

The Upgrade Risk of B3 Lesions to (Pre)Invasive Breast Cancer After Diagnosis on Core Needle or Vacuum Assisted Biopsy. A Belgian National Cohort Study

INTRODUCTION

Flat epithelial atypia (FEA), lobular neoplasia (LN), papillary lesions (PL), radial scar (RS) and atypical ductal hyperplasia (ADH) are lesions of uncertain malignant potential and classified as B3 lesions by the European guidelines for quality assurance in breast cancer screening and diagnosis. Current management is usually wide local excision (WE), surveillance may be sufficient for some. We investigated the upgrade rate of B3 lesions to breast malignancy in a subsequent resection specimen after diagnosis on core needle-or vacuum assisted biopsy (CNB-VAB) in a national population-based series.

METHODS

Using data from the Belgian Cancer Registry (BCR) between January 1, 2013 and December 31, 2016, inclusion criteria were new diagnosis of a B3 lesion on CNB or VAB with subsequent histological assessment on a wider excision specimen. Histological agreement between first- and follow-up investigation was analyzed to determine the upgrade risk to ductal adenocarcinoma in situ (DCIS) or invasive breast cancer (IC) according to the type of B3 lesion.

RESULTS

Of 1855 diagnosed B3 lesions, 812 were included in this study: 551 after CNB-261 after VAB. After diagnosis on CNB and VAB, we found 19.0% and 14.9% upgrade to malignancy respectively. Upgrade risks after CNB and VAB were: FEA 39.5% and 17.6%; LN 40.5% and 4.3%; PL 10.4% and 12.5%; RS 25.7%and 0.0%; ADH 29.5% and 20.0%.

CONCLUSION

Based on the observed upgrade rate we propose three recommendations: first, resection of ADH, and FEA with WE; second, resection of RS and classical LN with therapeutic VAB and further surveillance when radio-pathological correlation is concordant; third, surveillance of PL.

Abstract PD6-03: PD6-03 Serum methylmalonic acid concentrations at breast cancer diagnosis strongly correlate with frailty: a retrospective cross-sectional study

Introduction: Frailty commonly occurs in older persons, including those with breast cancer diagnoses. Methylmalonic acid (MMA), a metabolite and by-product of propionate metabolism, is known to increase significantly with aging. The relation between MMA concentrations and frailty is currently unknown. Objectives: A cross-sectional study was performed to study the association between baseline serum MMA concentrations and clinical frailty (estimated by G8 screening) in older patients with newly diagnosed breast cancer. Methods: 163 patients ≥70 years old with early-stage breast cancer were included (median age 76y). G8 screening and serum sample collection were performed at breast cancer diagnosis before any therapy was administered. MMA concentrations were measured via liquid chromatography with tandem mass spectrometry (LC-MS-MS). Results: MMA concentrations significantly increased with age (rs=0.3, p&lt;.0001) and serum creatinine levels (rs=0.5, p&lt;.0001) in this older population. The group with an abnormal G8 (≤14/17 = ‘frail’, 48% of patients) had significantly higher MMA levels than the group with normal G8 (&gt;14/17 = ‘fit’, 52%): 250nM vs. 189 nM, respectively (p=.0002). Higher MMA concentrations were independently associated with abnormal G8 (Odds ratio, 1.003, 95%CI 1.0 to 1.006, p=.04) after adjusting for age and serum creatinine levels. Among the different components of G8, MMA concentrations correlated most with weight loss (rs= -0.18, p=.02), mobility (rs= -0.23, p=.002), and polypharmacy (rs= -0.22, p=.005). Conclusion: Elevated serum MMA concentrations at breast cancer diagnosis are significantly associated, not only with age but also independently with clinical frailty in older patients with early-stage breast cancer. MMA may be further evaluated as a biomarker of frailty in older persons with breast cancer.

Citation Format: Qi Wu, Sigrid Hatse, Cindy Kenis, Yentl Lambrechts, Kevin Punie, Patrick Neven, Ann Smeets, Annouschka Laenen, Ana Gomes, Sarah-Maria Fendt, Hans Wildiers. PD6-03 Serum methylmalonic acid concentrations at breast cancer diagnosis strongly correlate with frailty: a retrospective cross-sectional study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD6-03.

Abstract P4-01-42: Pooled analysis of post-progression treatments after first-line ribociclib + endocrine therapy in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 studies

Background: The MONALEESA (ML) studies showed significant PFS & OS benefits for 1L ribociclib (RIB) + endocrine therapy (ET) in patients (pts) with pre/peri & postmenopausal advanced breast cancer. The benefit of RIB beyond study treatment (tx) was also observed, with improvements in PFS2 & delays in time to 1st subsequent chemotherapy (CT). While there is currently no preferred tx for the next line post-progression on a CDK4/6 inhibitor (CDK4/6i), except alpelisib in pts with a PIK3CA mutation, guidelines encourage multiple lines of ET or ET-based therapies before switching to CT (except for visceral crisis). This pooled exploratory analysis of the ML studies examined outcomes of various tx strategies post progression on RIB + ET.

Methods: Data from pts receiving 1L therapy in ML-2, -3, & -7 (NSAI cohort only & excluding pts with early relapse [≤ 12 mo after end of (neo)adjuvant ET] whose prognosis is closer to that of 2L pts) were pooled & pts receiving 1st subsequent therapies after progression were analyzed. Three groups of subsequent therapies were assessed: ET only, CT, & targeted therapy. Subsequent CT comprises CT +/- any other therapy; targeted therapy includes CDK4/6i, mTORi, PI3Ki, AKTi, etc, +/- ET. Subsequent CT & targeted therapy groups are mutually exclusive. Median duration of study tx, 1st subsequent therapy, & OS (from randomization to death) were analyzed by KM methods. Weighted Cox regressions were performed using inversed propensity scoring matching method (inverse probability tx weighting [IPTW]) to ensure compatible pt characteristics between tx arms. These are not randomized comparisons; only baseline characteristics were used for the estimation of propensity scores in the IPTW, imbalance of prognostic factors at progression may exist.

Results: Median follow-up time was 74 mo. 461 pts treated with RIB (81%) & 440 (86%) with PBO discontinued study tx & received a subsequent therapy. In the RIB arms, the most common 1st subsequent therapies were ET only (40%), CT (29%), combination with targeted therapy (28%), & other (4%); for the PBO arms, 34% received CT as a 1st subsequent therapy & 31% each received ET only or combination with targeted therapy (5% received other). In 14% & 20% of pts in the RIB & PBO arms, the 1st subsequent therapy was a CDK4/6i, of these 31% & 12% were RIB. In general, regardless of type of 1st subsequent therapy, the duration of both the study tx & the 1st subsequent therapy was longer for pts treated with RIB vs PBO (Table). In both RIB & PBO arms, pts who received subsequent CT had the shortest duration on study tx, whereas those who received subsequent targeted therapy combination had the longest. Among pts on 1L RIB + ET, after matching pre-randomization baseline characteristics, subsequent CDK4/6i use was associated with the longest mOS (84 [84-NE] mo), followed by ET only (60 [51-68] mo), then a non-CDK4/6i targeted therapy (52 [43-72] mo); post-progression CT was associated with the shortest mOS (37 [32-48] mo).

Conclusions: This large, pooled analysis of the ML studies shows that, in general, duration of any subsequent therapy was numerically longer post-1L RIB + ET vs PBO + ET, & subsequent CT was used less frequently for pts on RIB vs PBO. Both findings confirm that upfront tx with RIB does not worsen pt outcomes. This trend in enhancement of outcomes of subsequent therapies seen with 1L RIB suggests a post-tx effect that merits further exploration.

Abstract P3-05-28: Impact of increased adiposity on extended aromatase inhibitor treatment in postmenopausal patients with estrogen receptor positive (ER+) breast cancer: a retrospective analysis of the SOLE trial

Background: The risk of late distant recurrence (≥ 5 years) in post-menopausal patients with ER+ BC remains significant even after standard adjuvant endocrine therapy (ET). Obesity, which has reached high proportions in Western Countries, is one of the modifiable factors that can contribute to BC recurrences. While body mass index (BMI) is an easily available surrogate measure of adiposity, it might not reflect accurately patient adiposity, especially in post-menopausal patients. We therefore hypothesize that mammary adipocyte measurements might better capture the adiposity of the patient. In this study, we retrospectively evaluated the prognostic role of both BMI and adipocyte measurements in the SOLE trial.

Patients & Methods: The SOLE trial (NCT00553410) consisted of 4,884 postmenopausal women with hormone receptor positive, lymph node-positive BC treated with 5 years of letrozole after having completed 4-6 years of adjuvant ET. BMI was available for 3,606 patients with ER+/HER2- BC and categorized according to the WHO classification (underweight: &lt; 18.5, normal weight 18.5 – 24.9, overweight 25 – 29.9, obesity ≥ 30 kg/m2). Considering the small sample size, patients with underweight (n=35) were grouped together with patients with normal weight for the subsequent analyses. We evaluated the association between clinico-pathological characteristics and BMI using Fisher exact test and Kruskal-Wallis test. Given the previously reported association of BMI with distant recurrences (PMID: 21115856), we considered distant-relapse free interval (DRFI) as the main study endpoint. Cox regression analyses were adjusted for histology, chemotherapy (yes/no), type of local therapy, in addition to previously reported clinico-pathological variables (PMID: 29158011). Then, we conducted a stratified case-cohort study consisting of 311 patients (97 with distant relapse-cases) with successful digital assessment of adipocytes on normal mammary adipose tissue sample collected at surgery, as previously described (PMID: 33120083). Stratification factors were treatment arm and type of prior ET. Weighted Cox regression models (PMID: 17554753, 18712477) were used to evaluate prognostic association with adipocyte size (area in µm²) categorized in quartile of the 75th percentile (Q4 vs Q1-3), as done previously (PMID: 33753731).

Results: 1392 (39%) patients were normal weight, 1315 (36%) were overweight and 899 (25%) were obese. Older age at diagnosis, lymph node involvement (≥4), large tumor size and menopausal status were associated with overweight and obesity. After a median follow-up of 84 months, no associations were found between DRFI and BMI in the univariable and multivariable analysis (adjusted HR overweight vs normal=0.99, 95%CI: 0.76 – 1.29, p=0.977 and HR obese vs normal=1.11, 95%CI: 0.84 - 1.47, p=0.425). In the case-cohort study, patients with larger adipocytes had an increased hazard of distant recurrence in the univariable and multivariable analysis (see table 1).

Conclusion: In this study, we did not detect any association between BMI and survival outcomes. We however found that larger mammary adipocytes were independently associated with an increased hazard of distant recurrence. These results suggest that mammary adipocytes, which can be easily evaluated on H&E slides using digital pathology, should be considered as a novel marker to evaluate the risk of late recurrence in patients with breast cancer.

Abstract P5-02-14: Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials

Background: Genetic alterations that contribute to resistance to therapy may be acquired during treatment (tx) for hormone receptor−positive/human epidermal growth factor receptor−negative (HR+/HER2−) advanced breast cancer (ABC). A previous pooled analysis of circulating tumor DNA (ctDNA) in MONALEESA (ML)-2, -3, and -7 identified potential predictive biomarkers for response and resistance to ribociclib (RIB) at baseline (BL). Here, we describe an analysis of paired BL and end of treatment (EOT) samples from ML-2, -3, and -7 to identify acquired mechanisms that may impact resistance to RIB + endocrine therapy (ET) vs placebo (PBO) + ET. Methods: ML-2 (NCT01958021), ML-3 (NCT02422615), and ML-7 (NCT02278120) evaluated efficacy and safety of RIB + ET vs PBO + ET in pre- and postmenopausal patients (pts) with HR+/HER2− ABC treated in first-line (1L) and second-line (2L) settings. Plasma samples were collected at cycle 1 day 1 (C1D1; prior to first therapy exposure) and at EOT (± 28 days of recorded progression). ctDNA was sequenced using a targeted next-generation sequencing panel of ≈550 genes. Genes with an alteration frequency of &gt;5% at EOT, regardless of their frequency at BL, were included. Tumor mutational burden (TMB) was assessed by tx arm; a TMB cutoff of 10 mutations/MB was used to categorize pts as TMB high vs low. To assess differences in the presence of alterations, a McNemar test was performed on paired samples and adjusted (adj) for multiple testing using the false discovery rate (FDR). A Bayesian mixed effects model was used to account for ctDNA fraction and trial and to test for tx-specific resistance by including a tx × visit interaction term. Results: A total of 905 paired samples from ML-2, -3, and -7 were included in this analysis, 441 and 464 samples from pts treated with RIB + ET and PBO + ET, respectively. Overall, 17 genes had an alteration frequency of &gt;5% at EOT. The ctDNA fraction was higher at EOT vs C1D1 in both the RIB (P=.037) and PBO (P=.033) arms. The frequency of alterations in RB1 (10.4% vs 2.0%), ATM (11.3% vs 8.4%), FAT1 (4.8% vs 3.0%), and FAT3 (5.0% vs 2.5%) was higher at EOT vs C1D1 in the RIB arm (FDR-adj P&lt;.10). Alterations in ESR1 were also higher at EOT vs C1D1 in both the RIB (26.3% vs 9.1%) and PBO arms (28.9% vs 5.4%) (FDR-adj P&lt;.0001). Conversely, alterations in GATA3 were higher at EOT in the PBO arm (FDR-adj P=.11). These results were consistent after adjusting for ctDNA fraction. The most common ESR1 mutations were D538G, Y537S/N/C/D, E380Q, and L536H/P/R. Tx × visit interaction effects were observed for RB1 in the RIB arm and GATA3 in the PBO arm, suggesting tx-specific resistance. A tx × visit interaction for ESR1 was also observed, suggesting a larger relative increase in ESR1 mutations with PBO vs RIB. The percentage of pts with high TMB (&gt;10) at EOT increased from 1.1% to 5.7% in the RIB arm and from 1.7% to 3% in the PBO arm. After accounting for ctDNA fraction and trial, a larger numerical increase in TMB was observed for RIB (odds ratio [OR], 9.0; 95% CI, 2.9-32.7) vs PBO (OR, 2.1; 95% CI, 0.7-6.5); however, the model did not support a differential tx effect. Conclusions: This comprehensive analysis of pooled samples from ML-2, -3, and -7 identified acquired gene alterations in pts with HR+/HER2− ABC treated with 1L or 2L RIB + ET or PBO + ET. The frequency of several genes known to contribute to resistance (ESR1, RB1, ATM, FAT1, and FAT3) was higher at EOT vs C1D1 in pts treated with RIB + ET, while ESR1 and GATA3 alterations were higher at EOT vs C1D1 in pts treated with PBO + ET. This paired dataset of BL and EOT samples from pts with HR+/HER2− ABC treated with a CDK4/6 inhibitor and ET is the largest to date and could be used to validate and confirm acquired resistance mechanisms with low alteration frequency.

Citation Format: Fabrice Andre, Nadia Solovieff, Faye Su, Aditya Bardia, Patrick Neven, Yoon-Sim Yap, Debu Tripathy, Yen-Shen Lu, Dennis Slamon, Stephen K. Chia, Mukta Joshi, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Carlos Arteaga. Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-14.

Abstract PD13-11: PD13-11 Final Overall Survival Analysis of Monarch 2 : A Phase 3 trial of Abemaciclib Plus Fulvestrant in Patients with Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer

Background Abemaciclib is approved for patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC) with progression on prior endocrine therapy (ET). The MONARCH 2 trial showed a statistically significantly benefit in progression-free survival (PFS) (hazard ratio [HR]: 0.553; 95% CI: 0.449-0.681; p &lt; 0.001), overall survival (OS) (HR: 0.757; 95% CI: 0.606-0.945; p = 0.01) and a manageable safety profile for abemaciclib plus fulvestrant compared with fulvestrant alone. Here we report the pre-specified final overall survival (OS) analysis from the MONARCH 2 trial (NCT02107703). Methods MONARCH 2 was a global, randomized, placebo-controlled, double-blind phase 3 trial of abemaciclib or placebo, plus fulvestrant for treatment of pre-, peri- or postmenopausal women with CDK 4 & 6 inhibitor naïve HR+, HER2- ABC that progressed during ET. Pts were randomized 2:1 to receive abemaciclib or placebo, 150 mg twice daily, plus fulvestrant. Randomization was stratified based on site of metastasis (visceral, bone only, or other) and resistance to prior ET (primary versus secondary). OS and safety were key secondary endpoints, and chemotherapy-free survival was an exploratory endpoint defined as the time from randomization to initiation of chemotherapy or death, whichever occurs the earliest. Kaplan-Meier (KM) method was used to analyze time-to-event variables. A stratified Cox proportional hazards model was used to estimate treatment effect hazard ratio (HR). The prespecified final analysis was planned to occur based on approximately 441 OS events. Data cutoff was March 18, 2022. Results 669 women were randomized 2:1 to receive abemaciclib (n = 446) or placebo (n = 223), plus fulvestrant. Baseline characteristics have been previously reported (Sledge et. al., Jama Oncol 2020). The median follow-up time was approximately 80 months and at the time of the data cutoff, 11% of pts were still receiving study drug in the abemaciclib arm versus 2% in the placebo arm. 440 OS events were observed in the ITT population (abemaciclib arm: 283 events; placebo arm: 157 events). The median OS was 45.8 months in the abemaciclib arm and 37.2 months in the placebo arm (HR: 0.784; 95% CI: 0.644-0.955). The maintained separation of the KM curves beyond the medians is illustrated by the differences in the estimated 5- and 6-year OS rates between arms (5-year: 41.2% versus 29.2%; 6-year: 34.7% versus 23.7%; abemaciclib versus placebo respectively). While OS benefit was generally consistent across subgroups, a more pronounced benefit is noted in subgroups associated with a poorer prognosis such as visceral disease (HR: 0.643; 95% CI: 0.499-0.829), primary resistance to ET (HR: 0.634; 95% CI: 0.436-0.922) or negative progesterone receptor status (HR: 0.623; 95% CI: 0.405-0.959). Moreover, the addition of abemaciclib to fulvestrant deferred the initiation of chemotherapy (HR: 0.674; 95% CI: 0.562-0.809), with substantial difference in yearly chemotherapy-free survival rates (3 year: 42% vs 29.3%; 4 year: 37% vs 18.6%; 5 year: 32.4% vs 14.7%). Notably with longer exposure to abemaciclib, no new additional safety risks or cumulative toxicities were identified. Conclusions At the prespecified final OS analysis of the MONARCH 2 trial, with a median follow-up of 6.5 years, the statistically significant benefit previously demonstrated was confirmed and maintained. OS benefit was generally consistent across subgroups, with numerically greater effect size observed among patients with poorer prognosis. Importantly, the survival benefit came with a substantial extension of the chemotherapy-free survival time, which is an important consideration for pts with ABC. The results also provide assurance of the safety of abemaciclib with longer-term use.

Citation Format: Antonio Llombart-Cussac, George Sledge, Masakazu Toi, Patrick Neven, Joo Hyuk Sohn, Kenichi Inoue, Xavier Pivot, Meena Okera, Norikazu Masuda, Peter A. Kaufman, Han Koh, Eva-Maria Grischke, PierFranco Conte, Valerie Andre, Yuanyuan Bian, Ashwin Shahir, Gertjan van Hal. PD13-11 Final Overall Survival Analysis of Monarch 2 : A Phase 3 trial of Abemaciclib Plus Fulvestrant in Patients with Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD13-11.

Abstract P5-05-06: ctDNA detection in seven different types of body liquids in patients with metastatic breast cancer

Background. Liquid biopsies represent a less invasive alternative to tissue biopsy to characterize and possibly monitor the disease in patients with metastatic breast cancer. So far, blood remains the most frequently investigated body liquid in this context and the investigations mainly focus on the detection, quantification and characterization of the circulating tumor DNA (ctDNA). However, since blood might not capture the full disease profile, other sources of body liquids may have the potential to complement the information obtained from blood. The aims of the present study are therefore to assess whether: (i) ctDNA can be detected in different types of body liquids, and, (ii) the levels of ctDNA in a given liquid are associated with metastases in specific organs.

Patients and methods. Twelve patients from the post-mortem tissue donation program UPTIDER (NCT04531696) were included in this study. The receptor status of their primary tumor was: estrogen receptor negative, HER2 non-amplified (ER+/HER2-) (n=9), ER-/HER2- (n=2) and ER+/HER2+ (n=1). Median time between inclusion and death of the patient was 1.6 months (Interquartile range: [0.4-3.4]). Seven types of liquids were collected: blood, saliva, ascites, pleural fluid (PFL), cerebrospinal fluid (CSF), pericardial fluid and urine. Fluids were collected at study inclusion (blood, as well as saliva, urine, and ascites whenever possible) and at autopsy (except for saliva). In total, 108 liquid samples were collected and immediately centrifuged according to standard protocols. Cell free DNA (cfDNA) was extracted from the supernatant. All extracted cfDNA as well as germline DNA extracted from the 12 matched buffy coat samples underwent shallow whole genome sequencing. Log2 ratios were computed with CNVkit, and co-segmented per patient using the copynumber R package. Purity and ploidy were assessed by ABSOLUTE. Associations between organ involvement and ctDNA yield were assessed by Wilcoxon rank-sum tests. Samples at study inclusion and at autopsy were considered together unless otherwise specified.

Results. At the sample level, ctDNA could be identified in 54% of the samples. At the patient level, the proportion of liquid types in which ctDNA was detected was highly variable (median: 58%, IQR: 34-77%, Table 1). CtDNA was detected in ascites of all patients when investigated, in 78% of PFL, 73% of CSF, 67% of blood and 37% of pericardial fluid. Only for one patient with invasive lobular carcinoma, ctDNA was detected in saliva and urine, the latter most likely explained by invasion of the bladder. Of note, in 4/12 patients ctDNA could not be identified in blood but was detected in at least one of the other fluids for 3 of these patients. At autopsy, ctDNA levels tended to be higher in PFL, ascites, and CSF in case of pleural, peritoneal, and central nervous system (CNS) metastases respectively, reaching statistical significance only for PFL. In CSF, two patients have CSF ctDNA detected with no documented involvement of the CNS. No brain autopsy was however performed for these patients.

Conclusion. We have shown that ctDNA can be detected in all 7 different body liquids that were investigated in this study. The ctDNA levels in a given liquid can be associated with the presence of metastases in specific organs. Since ctDNA was not detected in 4 of our patients in blood but detectable for 3 of them in other liquids, the evaluation of additional sources of body fluids should be further investigated in patients with metastatic breast cancer. These results therefore open new avenues for the clinical monitoring and characterization of the disease.

Table 1. Summary of ctDNA detection per liquid type at the patient level based on the 108 evaluated samples. Histo.= Histological, ILC= Invasive lobular carcinoma, NA= not available, nr= number, NST= non-special type

Citation Format: François Richard, Tatjana Geukens, Maxim De Schepper, Amena Mahdami, Karen Van Baelen, Marion Maetens, Ha-Linh Nguyen, Anirudh Pabba, Sophia Leduc, Edoardo Isnaldi, Maysam Hajipirloo, Emily Vanden Berghe, Imane Bachir, Sigrid Hatse, Peter Vermeulen, Evy Vanderheyden, Bram Boeckx, Diether Lambrechts, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Hans Wildiers, Wouter Van Den Bogaert, Elia Biganzoli, Giuseppe Floris, Christine Desmedt. ctDNA detection in seven different types of body liquids in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-05-06.

Abstract P6-01-47: Stromal tumor infiltrating lymphocytes and pathological complete response in patients with inflammatory breast cancer treated with neoadjuvant chemotherapy

Background: Inflammatory breast cancer (IBC) is a rare (1-5%), but aggressive form of breast cancer (BC), accounting for ~10% of BC mortality. In early setting (M0), standard of care is neoadjuvant chemotherapy (NACT), followed by surgery. Nevertheless, outcome is still relatively poor. Pathological complete response (pCR) after NACT is prognostic in BC in general, and can be predicted by a high percentage of stromal tumor infiltrating lymphocytes (sTIL) in the primary tumor. The predictive value of sTIL in IBC has only been sporadically investigated, often in smaller series. Our aim was to determine which variables, including sTIL, are associated with pCR and to determine the prognostic value of pCR in IBC in a large multicentric, retrospective cohort. Patients & Methods: We included patients with IBC treated with NACT+/- anti-Human Epidermal growth factor Receptor 2 (HER2) therapy, followed by surgery from 10/1996 to 10/2021 in 7 different European hospitals. Clinicopathological variables were collected and central pathological review was performed, including sTIL scoring. This study focused on M0 cases. Considered clinicopathological variables were: age, histology, tumor grade, estrogen receptor status (ER), HER2 status, focality (unifocal vs not), and baseline locoregional nodal status (Table 1). Associations between pCR, clinicopathological variables and sTIL were assessed using Firth’s logistic regression models: Model 1 was adjusted for center, Model 2 additionally included all variables of interest. Similarly, linear regression was used to investigate the association between sTIL and clinicopathological features. Univariable and multivariable Cox regression was used to evaluate the role of pCR on disease free survival (DFS), distant recurrence free survival (DRFS) and overall survival (OS). DFS and DRFS were analyzed considering death without the respective event as competing risk. Results: 494 patients were included. The distribution according to receptor status was: ER-/HER2- (24.3%), ER+/HER2- (34.4%), ER+/HER2+ (13%) and ER-/HER2+ (20.2%). pCR rate was 26% and per receptor status: ER-/HER2- (28%), ER+/HER2- (10%), ER+/HER2+ (42%) and ER-/HER2+ (45%). pCR was associated with grade (G3 vs G1/2, OR =2.79 (1.70 − 4.74), p &lt; .001), ER-status (positive vs negative, OR = 0.39 (0.26 − 0.60), p &lt; .001) and HER2 status (positive vs negative, OR = 3.74 (2.43 − 5.81), p &lt; .001) in Model 1. Only the association with HER2 status remained significant in Model 2 (OR = 5.34 (2.83 − 10.47), p &lt; .001). sTIL was scored for 385 patients. Median sTIL was 5.3% [IQR 2.0%;16.7%] and according to receptor status: ER-/HER2- (10%), ER+/HER2- (2.5%), ER+/HER2+ (6.7%) and ER-/HER2+ (8.3%). Higher sTIL was associated with NST (p = .032), grade 3 (p = .015), and ER-negativity (p = .007) in Model 1. This was no longer significant in Model 2, but the direction of the trends was preserved. sTIL was associated with pCR (5% increment, OR = 1.13 (1.05 − 1.22), p = .002), but no longer after adjustment. No association between pCR and sTIL was found stratifying by receptor status. The median FU was 9.4 years and multivariable Cox regression models revealed that ER+ and HER2+ status and achieving pCR were significantly associated with better DFS, DRFS, and OS (Table 1). Conclusion: Our results indicate that patients with HER2+ tumors have a higher probability of achieving pCR and that pCR has an independent prognostic role in IBC. This is the largest IBC study with centrally scored sTIL, demonstrating that sTIL is associated with pCR but its role as an independent predictor of pCR is still not certain.

Citation Format: Maxim De Schepper, Ha-Linh Nguyen, François Richard, Florence Lerebours, Roman Vion, Florian Clatot, Anca Berghian, Marion Maetens, Sophia Leduc, Edoardo Isnaldi, Chiara Molinelli, Matteo Lambertini, Frederica Grillo, Gabriele Zoppoli, Luc Dirix, Hilde Wuyts, Kevin Punie, Hans Wildiers, Chantal Remmerie, Ann Smeets, Ines Nevelsteen, Patrick Neven, Anne Salomon, Denis Larsimont, Caroline Duhem, Patrice Viens, François BERTUCCI, Elia Biganzoli, Peter Vermeulen, Giuseppe Floris, Christine Desmedt. Stromal tumor infiltrating lymphocytes and pathological complete response in patients with inflammatory breast cancer treated with neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-47.

Abstract GS3-02: GS3-02 Camizestrant, a next generation oral SERD vs fulvestrant in post-menopausal women with advanced ER-positive HER2-negative breast cancer: Results of the randomized, multi-dose Phase 2 SERENA-2 trial

Background Camizestrant (C), a next-generation oral selective estrogen receptor (ER) antagonist and degrader (ngSERD) has shown promising clinical activity in ER+ breast cancer (BC) in the Phase 1 SERENA-1 study1,2 with a dose-dependent safety profile. The Phase 2 randomized SERENA-2 study (NCT04214288) initially assessed three doses of C vs fulvestrant (F) in post-menopausal women with ER+ HER2˗ BC with disease recurrence or progression after ≤1 endocrine therapy (ET) in the advanced setting.

Methods SERENA-2 evaluated efficacy and safety of C 75, 150 or 300 mg monotherapy QD vs F (per label). Eligible patients were randomized 1:1:1:1. The Primary objective was to determine clinical efficacy of C vs F by investigator-assessed progression-free survival (PFS). Secondary endpoints included objective response rate, response duration, clinical benefit rate at 24 weeks, overall survival and safety. Patients had no prior F or oral SERD and ≤1 ET and ≤1 chemotherapy (CTX) in the advanced setting. To assess the impact of prior CDK4/6 inhibitor (CDK4/6i) treatment, randomization was stratified so that 50% of patients had prior CDK4/6i. Planned enrolment of 288 patients began in April 2020. The C 300 arm was closed after 20 patients were enrolled, changing target enrolment to 236. By August 2021, 240 patients had been randomized. Primary analysis was triggered when 108 progression events (75% maturity) had occurred in the best performing pair (C vs F) in August 2022. Efficacy analyses compared C 75 and 150 mg doses with F, with no formal analyses of C 300 vs F. 108 events for pairwise comparison vs F gave 86% power at the 2-sided 10% significance level. Primary analyses used a Cox proportional hazards model to compare PFS, adjusting for prior CDK4/6i and lung/liver metastases. ESR1 mutations (ESR1m) were detected in plasma samples using next-generation sequencing.

Results 119/240 (49.6%) patients had had prior CDK4/6i therapy. At baseline, 88 (36.7%) patients had detectable ESR1m and 140 (58.3%) had lung/liver metastases. Prior CTX or ET rates in the advanced setting were 19.2 and 65.4%.

Treatment-emergent adverse events (AEs) (grade ≥3) occurred in 77.0 (12.2), 90.4 (21.9) and 68.5 (13.7) % of patients in the C 75, C 150 and F arms. AEs leading to treatment discontinuation occurred in 2.7, 0 and 0% of patients in the C 75, C 150 and F arms. The most common AEs considered by the investigator to be causally related to study drug were photopsia (18.4%) and (sinus) bradycardia (13.6%) – all were grade 1 or 2. Hot flush (2.7%) and myalgia (2.7%) were the most common AEs related to F.

Conclusions SERENA-2 is the first Phase 2 trial investigating multiple dose levels of an ngSERD vs F in post-menopausal women with advanced ER+ HER2˗ BC with disease recurrence or progression after ≤1 ET in the advanced setting. C at both 75 and 150 mg dose levels showed a statistically significant and clinically meaningful benefit in PFS vs F in the overall study population, and was well tolerated. The results of SERENA-2 support the further development of C in ER+ HER2- BC.

Acknowledgements

AstraZeneca sponsored this trial and funded medical writing support from Helen Heffron (InterComm International).

References

1. Baird R, Oliveira M, Ciruelos Gil EM, et al. SABCS 2020 Virtual Meeting. Abstract PS11-05; 2. Oliveira M, Hamilton EP, Incorvati J et al. ASCO 2022 Annual Meeting, Chicago, IL, USA. Abstract 1032.

Abstract HER2-16: HER2-16 Inter-lesion heterogeneity of HER2-status in metastatic breast cancer: possible implications for treatment with anti-HER2 antibody-drug conjugates

Background. Trastuzumab deruxtecan (T-DXd) has shown promising activity in patients with HER2-low metastatic breast cancer. As the HER2-status can vary between the primary and its corresponding metastases, treatment decisions should ideally be based on HER2 assessment of a recent biopsy. However, limited data is available on intra-patient inter-metastatic heterogeneity in HER2-status, affecting representability of a single biopsy and potential therapeutic options and outcome. We therefore assessed HER2 status on multiple metastases from patients with primary ER-positive/HER2-non-amplified breast cancer in our prospective post-mortem tissue donation program UPTIDER (NCT04531696). Methods. Ninety-one metastatic samples retrieved during the autopsies of 6 patients (range: 13–16/patient) and their respective primary tumours were immunohistochemically (IHC) stained for HER2 (HercepTestTM, RTU, ISO-15189 accredited) in our institution. Consensus scoring was performed between two pathologists according to ASCO/CAP 2018 guidelines. The observers were blinded for patient ID. Reflex fluorescence in situ hybridization (FISH) testing was performed for samples with IHC score of 2+. HER2 status was categorized as HER2-zero (IHC 0), HER2-low (IHC 1+ or IHC 2+ with negative FISH), or HER2-positive (IHC 3+ or IHC 2+ with positive FISH). To assess stability of the performance of IHC scoring in the post-mortem setting, an additional 13 samples taken from 3 metastases at regular (every 1.5h) time intervals during the autopsy underwent HER2 IHC scoring. Results. Evaluation of HER2-status in the primary tumour showed 2 patients with HER2-zero disease and 4 with HER2-low disease. A discordance between HER2 status of the metastases and their respective primary was seen in all patients. Not a single lesion was found to be HER2-positive. For every patient, at least one HER2-low metastasis was observed, with the percentage being highly variable between patients and ranging between 7 and 100%. No association was observed between HER2 status and organ site: HER2-low as well as HER2-zero lesions were found in all organs evaluated in at least 4 patients (liver, bone, pleura, lymph nodes). For 5 patients, multiple lesions within the liver were evaluated: while HER2-zero versus HER2-low status was concordant in those lesions in 4 patients, a mix of HER2 IHC scores was seen in 3 of them. IHC scores were stable over time for tumour lesions assessed repeatedly. Discussion. Important inter-lesion heterogeneity in terms of HER2-low status was observed in patients with primary ER-positive/HER2-non-amplified breast cancer participating to our post-mortem tissue donation program. This observed heterogeneity is unlikely to be due to post-mortem changes in HER2 expression. HER2-low status was found in at least one distant lesion in all patients, complicating therapeutic decision-making based on a single biopsy. Of note, IHC 1+ and 2+ scores varied between metastases of each patient too, making assessment on a single biopsy less reliable for stratification in clinical trials. Further assessment on samples from UPTIDER-patients with ER-negative disease is currently ongoing and results will be available to be presented.

Citation Format: Tatjana Geukens, Maxim De Schepper, François Richard, Marion Maetens, Karen Van Baelen, Amena Mahdami, Ha-Linh Nguyen, Edoardo Isnaldi, Sophia Leduc, Anirudh Pabba, Imane Bachir, Freya Mertens, Sara Vander Borght, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Hans Wildiers, Wouter Van Den Bogaert, Giuseppe Floris, Christine Desmedt. HER2-16 Inter-lesion heterogeneity of HER2-status in metastatic breast cancer: possible implications for treatment with anti-HER2 antibody-drug conjugates. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-16.

Abstract P1-02-04: Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score

Background The Regan Composite Risk Score (RCRS) is a web-based prognostic and predictive calculator to guide the use of adjuvant exemestane plus ovarian function suppression (AI + OFS) versus tamoxifen plus ovarian function suppression (TAM + OFS) or tamoxifen alone (TAM) for premenopausal women with hormone receptor-positive HER2-negative early breast cancer (HR+/HER2- EBC). We compared our adjuvant endocrine therapy policy based on the tumor board with the treatment guided by the RCRS during 2 time periods, one before and one after the acquaintance of the Tamoxifen and Exemestane Trial (TEXT) and Suppression and Ovarian Function Trial (SOFT) data. This allowed us to see a possible evolution in therapy policy. Methods A retrospective cohort study of 563 premenopausal patients with HR+/HER2- and HER2+ EBC diagnosed at the University Hospital of Leuven during 2 periods, 2010-2012 (cohort 1) and 2015-2017 (cohort 2), was conducted. For each patient with HER2- EBC, the RCRS was calculated by entering the requested characteristics in the online available tool. The primary outcome was to investigate how frequent our therapy differed from the therapy guided by the RCRS based on the estimated 8-yr distant relapse free interval (DRFI) with an arbitrary cut-off set at 3 %. If the received therapy was ≥ 3 % less efficient in 8-year DRFI compared to the optimal therapy according to RCRS, the patient was considered undertreated. If the received therapy differed by less than 3 % in 8-year DRFI compared to the optimal therapy according to RCRS and yet the most intensive therapy (AI + OFS &gt; TAM + OFS &gt; TAM) was administered, the patient was considered overtreated. In the other cases, the patient was considered to have been treated concordant with the RCRS. Secondarily, nonadherence of the HER2- and HER2+ patients towards the endocrine treatments leading to therapy switch because of intolerance was recorded at 6, 12, 24 and 36 months. Analyses were performed using SAS software and the comparison of both cohorts was performed by the chi-squared test for categorical variables. Results According to the RCRS, 43.2 % (89/206) of the HER2-negative patients of cohort 1 were undertreated compared to 22.1 % (43/194) in cohort 2 (chi- squared test, p-value &lt; 0.001). The number of overtreated patients also differed significantly between the two cohorts (chi-squared test, p-value = 0.003) with 2.9 % (6/206) in the first cohort and 10.3 % (20/194) in the second cohort. Finally, the number of patients treated concordant with the guidance derived from the RCRS was 53.9 % (111/206) in cohort 1 and 67.5 % (131/194) in cohort 2 (chi-squared test, p-value = 0.005). Treatment intolerance and switch was observed in 34.8 %, 16.7 % and 12.4 % of the patients receiving AI + OFS, TAM + OFS or TAM as initial therapy respectively; this was numerically higher for all treatments in cohort 2 vs cohort 1, although the observed difference was only significant for TAM. Conclusion In our center, a recent cohort of premenopausal women was more likely to be treated with the adjuvant endocrine treatment concordant with the guidance derived from the RCRS when using an arbitrary cut-off of 3 % to define a relevant improvement in outcome.

Citation Format: Charlotte Berteloot, Patrick Neven, Maja Vangoitsenhoven, Annouschka Laenen, Hans Wildiers, Kevin Punie, Ann Smeets, Ines Nevelsteen, Sileny Han, Thaïs Baert, Hilde Janssen, Eva Oldenburger, Adinda Baten, Patrick Berteloot, Rani Vanhoudt, Anne Deblander, Chantal Remmeriev, Christine Desmedt. Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-02-04.

Abstract PD4-06: PD4-06 Obesity-associated changes in transcriptomic profile and immune landscape of primary breast cancer revealed by bulk and single-cell gene expression data

Background: Breast cancer (BC) is one of the cancer types recognized as an obesity-associated disease. Current understandings of molecular mechanisms underlying the BC-obesity connection however largely came from experimental models while systematic investigation of the impact of obesity on BC biology in large patient series is still lacking. The purpose of this study is to discover changes in the transcriptomic profile of primary BC according to patients’ body mass index (BMI). Data and Methods: Bulk and single-cell gene expression data from treatment-naïve primary breast tumors from non-underweight patients were retrieved from the MINDACT trial (NCT00433589; N = 1481) and the pre-treatment cohort of the BioKey trial (NCT03197389, N = 36), respectively. Three categories were considered for BMI: lean, overweight and obese. The main analyses focused on the invasive carcinoma of no special type (NST) estrogen receptor-positive/HER2-negative (ER+/HER2-, N_bulk = 735, N_single-cell(sc) = 10) and NST ER-/HER2- (N_bulk = 118, N_sc = 15) subgroups. The bulk expression data was subjected to differential gene expression analyses according to BMI which was adjusted for menopausal status and tumor grade, then followed by gene set enrichment analyses. Clustering and cluster annotation were performed on the single-cell profiling data before differentially expressed genes according to BMI were identified for each of the present cell types. Results: Obesity-associated differences in the transcriptomic profile of breast tumors, which were subtle but potentially indicative of a biological relationship, were revealed by the bulk data. In both investigated subgroups, tumors from obese patients were shown to be enriched in cell cycle hallmarks. In ER-/HER2- tumors, adiposity further increased MYC signaling. We also observed different obesity-associated changes according to the ER status. Among ER+/HER2- tumors, those from obese patients were enriched in hallmarks related to inflammatory response compared to those from lean patients. In contrast, these hallmarks appeared to be enriched in the ER-/HER2- tumors from lean patients. Our investigation of the single-cell data further revealed shifts in the cell composition of tumor tissue and cell type-specific transcriptomic differences according to BMI which were more pronounced than those detected from the bulk data. ER+/HER2- tumors from obese patients have a higher frequency of immunosuppressive and pro-tumoral cell subpopulations such as dendritic cells (DC) enriched in immunoregulatory molecules (p = .03), LYVE1+ macrophages (p = .02) and myofibroblasts (p = .03) than those from lean patients. Overexpression of Cyclin D1 and CD24 was found in cancer cells in ER+/HER2- tumors from obese patients. A reduction in anti-tumor immune responses was evident with downregulation of multiple interferons in CD8+ and CD4+ T cells as well as B cells. We observed in the ER-/HER2- subgroup increased infiltration of plasmacytoid DC (p = .01), CCL2+ macrophages (p = .01) in tumors from obese versus lean patients, while fibroblasts showed an opposite tendency. Additionally, significant obesity-associated downregulation of major histocompatibility complex (MHC) molecules class I in cancer cells and MHC class II molecules in B cells could be suggestive of deficient antigen presentation and activation of cytotoxic and helper T cells. Conclusion: We highlighted the impact of obesity on the remodeling of tumor and tumor microenvironment which might generally lead to a suppression of anti-tumor immune responses, albeit potentially via diverse axes according to the ER status. Although investigation on a larger cohort is warranted, our current results suggest that obesity-associated transcriptomic changes in BC could be highly cell type-specific, hence we recommend single-cell approaches in addition to spatial multi-omics analysis to further elucidate the interplay between obesity and BC.

Citation Format: Ha-Linh Nguyen, Tatjana Geukens, Marion Maetens, Karen Van Baelen, Maxim De Schepper, Coralie Poncet, Mauro Delorenzi, Marjanka K. Schmid, Emiel Rutgers, Laura Van ’t Veer, Martine Piccart, Fatima Cardoso, Giuseppe Viale, Ayse Bassez, Hanne Vos, Patrick Neven, Ines Nevelsteen, Kevin Punie, Hans Wildiers, Giuseppe Floris, Diether Lambrechts, Ann Smeets, Elia Biganzoli, François Richard, Christine Desmedt. PD4-06 Obesity-associated changes in transcriptomic profile and immune landscape of primary breast cancer revealed by bulk and single-cell gene expression data [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD4-06.

Abstract P3-05-40: Association of body mass index with clinicopathological features and survival in patients with primary ER+/HER2- invasive lobular breast cancer

Background: Invasive lobular carcinoma (ILC) represents up to 15% of all breast carcinomas. The majority of ILC express the estrogen receptor (ER) and have no amplification/overexpression of the human epidermal growth factor receptor 2 (HER2). A high body mass index (BMI) has been associated with an increased risk of developing ILC in postmenopausal women, similar to what is seen for breast cancer of no special type (NST). It is however unknown if BMI impacts the clinicopathological features and the prognosis of ILC.

Methods: We performed a multicentric retrospective study in 5 European centers of patients diagnosed between January 2000 and December 2020 with ER+/HER2- non-metastatic pure (i.e., not mixed) ILC. Patient and tumor characteristics and event-related data were collected. BMI was categorized into underweight (≤18.5kg/m2), lean (&gt;18.5kg/m2 and &lt; 25kg/m2), overweight (≥25kg/m2 and &lt; 30kg/m2) and obese (≥30kg/m2). The association of BMI as either a continuous or a categorical variable with clinicopathological variables was assessed using linear regression or ordinal logistic regression, respectively. Median follow-up was calculated using the reverse Kaplan-Meier estimator. Survival analyses using univariable (stratified by center) and multivariable (adjusted for all included variables and stratified by center) Cox regression were performed to evaluate the association of BMI with disease free survival (DFS), distant recurrence free survival (DRFS) and overall survival (OS). DFS and DRFS were analyzed in the presence of death without event as the competing risk.

Results: The data of 2476 patients were collected and BMI was available for 2346 patients. In total, 1299 (55%) patients were lean, 638 (27%) overweight and 339 (14%) obese. Underweight patients only represented 3% of all patients and were thus excluded from further analyses. A higher age at diagnosis, higher grade, larger tumor size, nodal involvement and multifocality were significantly associated with higher BMI (Table 1). The median follow-up was 8,5 years (interquartile range 59.24 – 142.13 months). In univariable analysis, higher BMI was associated with worse survival outcomes (Table 2). However, this association was not seen in multivariable analysis while grade, tumor size and nodal involvement were still prognostic for all endpoints. Similar results were seen with BMI as a continuous variable.

Conclusion: Larger tumors and nodal involvement were more likely to be found in patients with ER+/HER2- ILC with higher BMI which might be explained by a delayed diagnosis in these patients. Higher grade also seemed to be associated with higher BMI. In multivariable analyses, BMI was not found to be an independent prognostic factor. Tumor grade, tumor size, and nodal status remained strongly prognostic for survival outcomes in multivariable survival analyses which is consistent with their known prognostic importance in luminal tumors. We hypothesize that the prognostic effect of BMI is mediated through these variables for patients with ER+/HER2- ILC.

Table 1. Association of clinicopathological features of ER+/HER2- ILC with categorical BMI.

Table 2. Association of categorical BMI and other clinicopathological features of ER+/HER2- ILC with survival.

Citation Format: Karen Van Baelen, Ha-Linh Nguyen, François Richard, Anne-Sophie Hamy, Aullène Toussaint, Fabien Reyal, Anne Salomon, Luc Dirix, Peter Vermeulen, Hilde Wuyts, Maria Karsten, Adam D. Dordevic, Guilherme Nader Marta, Evandro de Azambuja, Christos Sotiriou, Denis Larsimont, Ottavia Amato, Marion Maetens, Maxim De Schepper, Tatjana Geukens, Sileny Han, Thaïs Baert, Kevin Punie, Hans Wildiers, Chantal Remmerie, Ann Smeets, Ines Nevelsteen, Giuseppe Floris, Elia Biganzoli, Patrick Neven, Christine Desmedt. Association of body mass index with clinicopathological features and survival in patients with primary ER+/HER2- invasive lobular breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-40.

Abstract P3-05-35: The impact of parity and age of first full term pregnancy on the prevalence of invasive lobular carcinoma in patients with breast cancer

Background: The impact of reproductive factors on breast cancer has proven to be complex. The risk for estrogen receptor positive/HER2-negative (ER+/HER2-) breast cancer is estimated to be transiently augmented in the years after giving birth (up to 20 years) while later in life high parity and early first full-term pregnancy (1st FTP) seem to protect against ER+/HER2- breast cancer (BC). Invasive lobular carcinomas (ILC) represents the second most common histological subtype of BC and &gt;90% are ER+/HER2-. In this study, we aimed at investigating whether parity and age at 1st FTP are associated with: 1) the prevalence of ER+/HER2- pure ILC (i.e., not mixed) in an ER+/HER2- BC cohort (overall and according to the age at breast cancer diagnosis), and, 2) standard clinical and pathological features of pure ILC.

Patients and methods: We performed a single center retrospective study in UZ Leuven, Belgium of patients diagnosed with non-metastatic ER+/HER2- breast cancer between January 2000 and November 2020. Both patient and tumor characteristics were collected from clinical files. Firth’s logistic regression was performed to investigate the association of BC histology (pure ILC vs all other BC histological subtypes = control group) with parity (yes vs. no and nulliparous, 1 child, 2 children, &gt;2 children) in univariable models and multivariable models adjusted for age group at diagnosis (&lt; 30, 31-40, 41-50, 51-60, 61-70, &gt;70), age at 1st FTP (continuous and per age group: &lt; 21, 21-25, 26-30, &gt;30), Interval between 1st FTP and diagnosis (continuous), year of birth and BMI. Analyses were done in the overall group as well as per age group at diagnosis. Similarly, regression analyses were performed in patients with ER+/HER2- ILC to assess the association of parity (yes vs. no and nulliparous, 1 child, 2 children, &gt;2 children) with the following variables: age at diagnosis, BMI, histological grade, tumor size, nodal involvement and progesterone receptor positivity.

Results: 7360 patients were included of which 1121 (15.2%) were diagnosed with pure ER+/HER2- ILC, the remaining 6239 (84.8%) patients were considered as the control group. Overall, in multivariable analyses, parity with &gt;2 children was associated with a higher prevalence of pure ILC as compared to uniparous patients (odds ratio, OR 1.257, 95CI 1.039-1.521, p= 0.019). No significant association was seen for age at 1st FTP and interval 1st FTP – diagnosis. The subgroup analyses per age group are summarized in Table 1. Only for the age group 41-50, an increased age 1st FTP was associated with an increased prevalence of pure ILC. In patients with pure ER+/HER2- ILC, nulliparous women were less likely to have a progesterone receptor (PR)-positive tumor as compared to parous women (OR 0.477, 95CI 0.224-0.907, p= 0.022). No other significant associations were seen for clinicopathological features between nulliparous and parous women, and between uniparous and multiparous women in the overall cohort nor any age group.

Conclusions: Within an ER+/HER2- breast cancer cohort, higher parity seems to be associated with a higher prevalence of pure ILC, which is especially seen in the patients diagnosed with breast cancer between the age of 51 and 60. Increased age at the 1st FTP only seems to increase the incidence of ILC in the age group 41-50. With the exception of nulliparous women having less PR positive tumors, parity does not seem to affect the clinicopathological features of ER+/HER2- pure ILC.

Table 1: subgroup analyses per age group of association of histology (pure ILC vs control group) with parity, age 1st FTP and interval 1st FTP – diagnosis

Citation Format: Karen Van Baelen, Ha-Linh Nguyen, François Richard, Maja Vangoitsenhoven, Giuseppe Floris, Hans Wildiers, Kevin Punie, Ann Smeets, Ines Nevelsteen, Frédéric Amant, Sileny Han, Thaïs Baert, Patrick Neven, Christine Desmedt. The impact of parity and age of first full term pregnancy on the prevalence of invasive lobular carcinoma in patients with breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-35.

Abstract P6-14-14: Advancing research on metastatic breast cancer: the UPTIDER post-mortem tissue donation program

Background. Research in metastatic breast cancer is hampered by limited sample availability. Post-mortem tissue donation programs can help to overcome this problem but are logistically challenging and have thus far mainly focused on histopathological and genomic research. We here present the UPTIDER program (NCT04531696), aimed at the multilevel characterization of advanced breast cancer and generation of tumour models. Patients and Methods. Patients with stage IV breast cancer receiving their last line(s) of treatment are eligible for participation. Blood, urine and saliva samples are collected upon inclusion. Upon death, a post-mortem MRI (when possible) followed by a rapid autopsy is performed. Liquid biopsies from all body fluids and tissue samples from all macroscopically identified metastatic sites are collected. Samples are processed as mirrored biopsies in different conditions, such as fresh frozen for omics analyses, formalin fixed paraffin-embedded for histopathology, and slowly frozen in freezing medium or fresh for generation of xenograft and organoid models. Results. Since approval by the local Ethical Committee in November 2020, 22 patients have been enrolled and 15 autopsies have been performed. Mean interval between death and start of autopsy was 3h (range 2-6h), mean duration of the autopsies was 6h (4-9h). A post-mortem MRI was performed in 6 patients. Peripheral blood, central blood and bone marrow were collected from all patients; urine, ascites, cerebrospinal, pericardial and pleural fluid all in more than 2/3 of patients. On average, 232 (range 90-406) tissue samples of which 164 (45-303) pathological from 42 (15 – 79) metastases were collected for each patient. Most often sampled metastatic sites were lymph nodes, liver, bones, pleura and peritoneum. Samples from the primary tumour could be retrieved from all patients, either during the autopsy (n=6) or from historical archives. In total, 133 tumour samples were sent to collaborating partners for patient-derived xenograft creation. Already some have been successfully established and stored, including models derived from a patient with invasive lobular carcinoma (ILC) and one with metaplastic squamous cell carcinoma. When correlating microscopic and macroscopic findings, patients could largely be divided into three main categories. Eleven patients presented with overt and extensive disease burden, often characterized by diffuse visceral, pleural, peritoneal, bone and lymph node involvement. Two patients, both with ILC, presented with underestimated yet extensive disease burden. While gross examination and cross sectioning of organs did not reveal clear involvement, microscopical invasion of stomach and liver, amongst others, was found. Lastly, limited disease burden was seen in two patients, both with leptomeningeal involvement. In those patients, massive tumoral infiltration in the subarachnoid space and along the blood-brain barrier was seen microscopically, with no grey matter invasion. Conclusion. We successfully launched a new and comprehensive post-mortem tissue donation program for patients with metastatic breast cancer, enrolling ~ 1 patient per month. Post-mortem tumour samples already resulted in successful establishment of some patient-derived xenografts. From a clinical point of view, vast underestimation of the disease extent on imaging during life as well as macroscopically during the autopsy was observed in some patients with metastatic ILC. For patients with leptomeningeal metastasis, we showed that the highly aggressive nature of their disease might be explained by extensive meningeal infiltration disrupting the blood-brain barrier. Further insights into disease progression and heterogeneity will be generated by the ongoing multi-omics analyses.

Citation Format: Tatjana Geukens, Maxim De Schepper, Karen Van Baelen, François Richard, Marion Maetens, Amena Mahdami, Ha-Linh Nguyen, Edoardo Isnaldi, Anirudh Pabba, Sophia Leduc, Imane Bachir, Maysam Hajipirloo, Emily Vanden Berghe, Sigrid Hatse, Eleonora Leucci, Maria Francesca Baietti, Georgios Sflomos, Cathrin Brisken, Patrick Derksen, Colinda Scheele, Vincent Vandecaveye, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Elia Biganzoli, Hans Wildiers, Wouter Van Den Bogaert, Giuseppe Floris, Christine Desmedt. Advancing research on metastatic breast cancer: the UPTIDER post-mortem tissue donation program [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-14-14.

Abstract GS1-09: Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes

Background Adjuvant abemaciclib (a CDK4 and 6 inhibitor) combined with ET resulted in significant and clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in patients (pts) with HR+, HER2-, node-positive, high risk EBC in the monarchE trial, and is an approved adjuvant therapy for these patients. Here we present efficacy results from a pre-specified overall survival interim analysis (OS IA2) which was planned to occur 2 years (yrs) after the primary outcome analysis. Methods Pts were randomized (1:1) to receive ET for up to 10 yrs +/- abemaciclib for 2 yrs (study treatment period). High-risk EBC was defined as either ≥4 positive axillary lymph nodes (ALN), or 1-3 ALN with either Grade 3 disease and/or tumor ≥5 cm (Cohort 1). While the proliferation biomarker Ki-67 was centrally assessed in all pts with available tissue sample, an additional smaller group of pts with 1-3+ ALN and central Ki-67 ≥20% as the only high-risk feature were included (Cohort 2). The intent-to-treat (ITT) population consisted of both Cohort 1 (5120 pts) and Cohort 2 (517 pts). Hazard ratios (HR) were estimated using Cox proportional hazard model. Results At a median follow-up of 42 months, all pts were off abemaciclib. IDFS and DRFS data illustrate a sustained benefit beyond the treatment period. In the ITT population, the HR for IDFS was 0.664 (95% CI: 0.578, 0.762) and DRFS was 0.659 (95% CI: 0.567, 0.767). At 4 yrs, this reflected an improvement in IDFS rates from 79.4% to 85.8% (absolute difference 6.4%), and in DRFS rates from 82.5% to 88.4% (absolute difference 5.9%). The continued separation of the curves was associated with an increase in absolute benefit in IDFS 4-year rates compared to 2-and 3-year IDFS rates (absolute difference 2.8% and 4.8% respectively). While OS remained immature, there was a lower number of deaths observed in the abemaciclib plus ET arm compared to the ET alone arm (157 [5.6%] vs 173 [6.1%], HR 0.929 [95% CI: 0.748, 1.153], p = 0.503), suggesting that the robust benefit in IDFS and DRFS began to translate into a numerically favorable OS HR. As previously described, within Cohort 1, a Ki-67 index of ≥20% was associated with a worse prognosis, but similar abemaciclib treatment effects were observed regardless of Ki-67 index. No new safety signals were observed. Conclusion The clinically meaningful benefit of adjuvant abemaciclib added to ET in HR+, HER2-, node-positive, high-risk EBC persists beyond completion of abemaciclib therapy, yielding an increase in absolute IDFS and DRFS benefit at 4 yrs. While OS remains immature at this time, the lower number of deaths in the abemaciclib arm compared to the ET arm suggest that a survival signal favoring abemaciclib is emerging.

Citation Format: Stephen Johnston, Masakazu Toi, Joyce O’Shaughnessy, Priya Rastogi, Mario Campone, Patrick Neven, Chiun Sheng Huang, Jens Huober, Georgina Garnica Jaliffe, Irfan Cicin, Sara Tolaney, Matthew P. Goetz, Hope Rugo, Elżbieta Senkus, Laura Testa, Lucia Del Mastro, Chikako Shimizu, Ran Wei, Ashwin Shahir, Maria Munoz, Belen San Antonio, Valerie Andre, Nadia Harbeck, Miguel Martín. Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr GS1-09.

Abstract P6-10-06: A preoperative window-of-opportunity study of imlunestrant in estrogen receptor-positive, HER2-negative early breast cancer: Results from the EMBER-2 study

Background: Imlunestrant is a novel, orally bioavailable selective estrogen receptor degrader (SERD) with pure antagonistic properties that result in sustained inhibition of estrogen receptor (ER)-dependent gene transcription and cell growth. In a phase 1 study, imlunestrant monotherapy showed favourable safety, pharmacokinetics (PK) and preliminary efficacy in heavily pre-treated ER-positive (ER+) advanced breast cancer patients (Jhaveri ASCO 2022). Here, we present pharmacodynamic (PD) data from the preoperative window of opportunity (WOO) study (EMBER-2, NCT04647487), evaluating the biological activity of imlunestrant monotherapy in ER+, HER2-negative (HER2-) early breast cancer (EBC).

Methods: Post-menopausal women with stage I–III operable ER+ (&gt;50%) or Allred score &gt;5, HER2- untreated EBC ≥1 cm in diameter were randomized 1:1 to imlunestrant 400 mg once daily (QD) or imlunestrant 800 mg QD for 15 days (treatment window of -2 to +7 days) up to the surgery date. Pre- and on-treatment tumor samples were compared for changes in PD biomarkers. Primary study objective was change in ER expression (measured by IHC and quantified by H-score). Secondary objectives were change in progesterone receptor (PR) expression (measured by IHC and quantified by H-score) and Ki-67 (measured by IHC and expressed by percentage positive scoring) along with evaluation of safety and tolerability.

Results: From Apr 28, 2021, to Mar 11, 2022, 58 patients were enrolled of which 54 were biomarker-evaluable for ER expression (400 mg: n = 28; 800 mg: n = 26). Patient demographics and tumor characteristics for all enrolled patients were similar across cohorts, with a median age of 64 years (50-83), 72% invasive ductal carcinoma (IDC), 28% invasive lobular carcinoma (ILC), 59% stage I, 36% stage II and 5% stage III disease. 91% of the patients had a compliance rate higher than 80%. Among biomarker evaluable patients, relative reduction in PD biomarkers after a median of 15 days (range 13 to 23 days) of treatment are presented in Table 1. There was no significant difference in PD biomarker modulation noted between the two imlunestrant doses (400 mg vs 800 mg) or based on tumor histology (IDC, ILC). Imlunestrant was well tolerated. There were no discontinuations due to adverse events (AEs). Treatment-related AEs (TRAEs) were mainly grade 1, most commonly: fatigue (10%), diarrhea (9%), hot flushes (7%), and nausea (5%). There were no TRAEs of diarrhea and nausea observed at the 400 mg dose. No grade 3 or higher TRAEs were reported.

Conclusion: Imlunestrant demonstrated evidence of target engagement along with consistent biological activity across all evaluated dose levels and was well tolerated in an EBC population, further supporting continued adjuvant development in the ongoing EMBER-4 study. Additional biomarker analyses for the EMBER-2 study are also planned.

Table 1. Relative reduction in PD biomarkers from Baseline to Day 15

Citation Format: Patrick Neven, Nicole Stahl, Maria Vidal, Miguel Martín, Nadia Harbeck, Peter A. Kaufman, Francois-Clement Bidard, Peter A. Fasching, Philippe Aftimos, Erika Hamilton, Stacey Carter, Peter Schmid, Duncan Wheatley, Manali Bhave, Kelly K. Hunt, Swati A. Kulkarni, Roohi Ismail-Khan, Claudia Karacsonyi, Shawn T. Estrem, Umut Ozbek, Bastien Nguyen, Eva Ciruelos. A preoperative window-of-opportunity study of imlunestrant in estrogen receptor-positive, HER2-negative early breast cancer: Results from the EMBER-2 study. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-06.

Abstract P2-11-18: Serum methylmalonic acid concentrations at breast cancer diagnosis are not associated with distant metastases

Introduction: Methylmalonic acid (MMA), a metabolite and by-product of propionate metabolism, promotes breast cancer (BC) progression in mice via the transforming growth factor-beta (TGFβ) signaling pathway (Gomes et al, Nature 2020). It is currently unknown if this effect also exists in patients with BC. Objectives: To investigate the association between baseline serum MMA concentrations in patients at BC diagnosis and development of distant metastases via a matched case-control study. Methods: We included 32 patients with early Luminal B-like BC (Lumb, median age 62.4y) and 52 patients with early triple-negative BC (TNBC, median age 50.5y) who developed distant metastases within 5 years. They were matched to an equal number of early BC patients with at least 5 years of follow-up (median age 62.2y for Lumb and 50.5y for TNBC) who did not develop distant metastases with at least 5 years of follow-up. Matching was performed based on age at diagnosis date (± 5y), tumor stage, and treatment received ((neo)adjuvant chemotherapy and radiotherapy, yes/no). Serum MMA concentrations were determined by liquid chromatography with tandem mass spectrometry (LC-MS-MS). Summary statistics, paired analyses, and multiple conditional logistic regression analyses were performed with and without adjusting for potential covariates (age, kidney function, and tumor stage). Results: Baseline serum MMA at BC diagnosis significantly correlated with age (rs=0.35, p=.005 in Lumb; rs=0.35, p=.0003 in TNBC), and negatively correlated with kidney function assessed by estimated glomerular filtration rate (eGFR, rs= -0.42, p=.0005 in Lumb; rs= -0.32, p=.0009 in TNBC). MMA concentrations at diagnosis were not associated with distant metastases in either subtype, after adjusting for kidney function, age, and tumor stage (all p&gt;.05). Next, we categorized BC cases in the public TCGA (n=174 for Lumb; n=140 for TNBC), METABRIC (n=461 for Lumb; n=199 for TNBC), and GSE25066 (n=78 for Lumb; n=182 for TNBC) database according to their 5-year metastatic status, and analyzed the TGFβ signaling pathway activity of primary BC. Like MMA concentrations, a gene expression signature of TGFβ signaling was not associated with distant metastases in patients with BC. Conclusion: Baseline serum MMA concentrations and a gene signature for TGFβ signaling at BC diagnosis are not associated with distant metastases among patients with Lumb and TNBC subtypes.

Citation Format: Qi Wu, Sigrid Hatse, Juan F. García, Patricia Altea-Manzano, Jaak Billen, Mélanie Planque, Anke Vandekeere, Yentl Lambrechts, François Richard, Annouschka Laenen, Kevin Punie, Patrick Neven, Ines Nevelsteen, Giuseppe Floris, Christine Desmedt, Ana Gomes, Sarah-Maria Fendt, Hans Wildiers. Serum methylmalonic acid concentrations at breast cancer diagnosis are not associated with distant metastases [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-11-18.

Abstract GS3-01: GS3-01 EMERALD phase 3 trial of elacestrant versus standard of care endocrine therapy in patients with ER+/HER2- metastatic breast cancer: Updated results by duration of prior CDK4/6i in metastatic setting

Background: In patients (pts) with ER+/HER2− metastatic breast cancer (MBC) following progression on prior endocrine and CDK4/6i therapy, the EMERALD trial demonstrated significantly prolonged progression-free survival (PFS) and a manageable safety profile for elacestrant versus standard of care endocrine therapy (SoC). Benefit was observed in all pts and in pts with ESR1 mutant MBC (ESR1-mut). EMERALD is the only oral SERD monotherapy pivotal trial where all pts were pretreated with CDK4/6 inhibitor (CDK 4/6i). Here, we examine the impact of duration of prior CDK4/6i on PFS.

Methods: EMERALD (NCT03778931) is a randomized, open-label, phase 3 trial that enrolled pts with ER+/HER2- MBC who previously had 1-2 lines of endocrine therapy, mandatory CDK4/6i, and ≤1 chemotherapy; prior treatment with fulvestrant was allowed. Patients were randomized 1:1 to elacestrant (400 mg orally daily) or SoC (investigator’s choice of aromatase inhibitor or fulvestrant). If randomized to the control arm, patients who received prior fulvestrant were to receive an aromatase inhibitor, and vice versa. If two CDK4/6i were used in the metastatic setting (n=40), the cumulative duration was calculated.

Results: A total of 478 pts were randomized (228 with ESR1-mut) between Feb 2019 – Oct 2020 (n=239, elacestrant; n=239, SoC). Overall survival was not yet mature, as of September 2nd 2022. Updated PFS results show statistically significant results in favor of elacestrant, both in all pts and in pts with ESR1-mut. The duration of prior CDK4/6i in the metastatic setting was positively associated with PFS, the longer the duration of prior CDK4/6i in the metastatic setting (n=465), the longer the PFS on elacestrant versus SoC (Table 1).

Updated safety data were consistent with previously reported results. Most of the adverse events (AEs), including nausea, were grade 1 and 2, and only 3.4% and 0.9% of the pts discontinued trial therapy because of an AE on elacestrant and SoC, respectively. A low percentage of pts received an antiemetic; 8.0%, 3.7%, and 10.3%, on elacestrant, fulvestrant, and AI, respectively. No hematological safety signal was observed and none of the patients in either of the two treatment arms had sinus bradycardia.

Conclusions: EMERALD is the first phase 3 trial to demonstrate a significant PFS improvement versus SoC in all pts and in the subgroup with ESR1 mutations in pts with ER-positive/HER2-negative MBC with 1-2 prior lines of endocrine treatment ± one line of chemotherapy. Elacestrant demonstrated longer PFS versus SOC that was positively associated with the duration of prior treatment with CDK4/6i, which was more pronounced in pts with ESR1-mut MBC. In this 2nd and 3rd line setting, elacestrant was well tolerated with significantly longer PFS versus SoC, highlighting its potential role as a therapeutic option for pts with ER+/HER2- MBC.

Table 1: PFS estimates in the elacestrant and SoC arms based on different cut-off points for the duration of prior CDK4/6i.

Citation Format: Aditya Bardia, Francois-Clement Bidard, Patrick Neven, Guillermo Streich, Alberto J. Montero, Frederic Forget, Marie-Ange Mouret-Reynier, Joo Hyuk Sohn, Donatienne Taylor, Kathleen K. Harnden, Hung Khong, Judit Kocsis, Florence Dalenc, Patrick Dillon, Sunil Babu, Simon Waters, Ines Deleu, Jose Angel García-Sáenz, Emilio Bria, Marina Elena Cazzaniga, Philippe Aftimos, Javier Cortés, Giulia Tonini, Tarek Sahmoud, Nassir Habboubi, Krzysztof Grzegorzewski, Virginia Kaklamani. GS3-01 EMERALD phase 3 trial of elacestrant versus standard of care endocrine therapy in patients with ER+/HER2- metastatic breast cancer: Updated results by duration of prior CDK4/6i in metastatic setting [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr GS3-01.

Abstract P4-03-20: Association between reproductive factors (parity and age first full term birth) and the frequency of estrogen receptor negative breast cancer according to age at diagnosis

Background: The frequency of early estrogen receptor (ER)-negative breast cancers (BC) decreases with increasing age at diagnosis (Partridge P, JCO 2016). Giving birth is generally considered a protective factor for the occurrence of BC in a woman’s lifetime. However, for up to more than 20 years following childbirth, BC risk may be higher. This appears to be due to an increase in hormone receptor-positive BC, especially in women older at the time of 1st childbirth (Nichols HB, Ann Int Med 2019). This means that the ER-negative BC are relatively less frequent in these 2 decades after delivery. In this study, we aimed at retrospectively investigating the impact of parity and age at first full term pregnancy (FFTP) on the frequency of ER-negative BC according to the age at diagnosis in a large institutional cohort of patients diagnosed with BC.

Patients and Methods: We considered all patients diagnosed and/or treated with early BC in UZ Leuven between January 2000 and November 2020. ER-negativity was defined as &lt; 1% positive cells. Age at diagnosis was subdivided in categories of 5 years. Parous women could be having a low (1 or 2 children) or high parity (&gt; 2 children) and age of FFTP was arbitrarily divided into &lt; or ≥ 27 years of age. BMI was considered a possible confounder and was corrected for. A logistic regression model was used for data analysis with ER-negative status as binary outcome and FFTP class and multiparity as explanatory variables. To test whether the difference in ER-negative proportions between FFTP classes depends on multiparity, we modelled the interaction between multiparity and FFTP class.

Results: We included 9955 consecutive female patients after excluding missing values. 8358 out of 9955 women had at least 1 child (84%). In our study population, parity as such was not an independent variable for BC subtype. Women with a FFTP ≥ 27y as compared to those with a FFTP &lt; 27y were less likely to have an ER-negative BC. The p-value for the interaction term between high parity (&gt;2 children) and FFTP class equals p= 0.0044. Hence, there is statistical evidence to suggest that the differences between FFTP categories with regards to ER-negative BC may depend on multiparity. Table 1 shows a lower incidence of ER-negative BC in the FFTP ≥ 27y group compared to the FFTP &lt; 27y group in case of high parity. Table 2 shows the absolute proportion. These results seem to be independent of BMI.

Conclusion: Women with a FFTP at 27 years of age or older and more than 2 children have proportionally less ER-negative type breast cancers as compared to women with a FFTP before 27 years of age. This difference between FFTP classes is not observed in absence of high parity.

Table 1: effect of FFTP class by multiparity

Table 2: proportion of ER-negative breast cancer subtype

Citation Format: Maja Vangoitsenhoven, Evert Theys, Karen Van Baelen, Annouschka Laenen, Christine Desmedt, Giuseppe Floris, Hans Wildiers, Kevin Punie, Sileny Han, Thaïs Baert, Frédéric Amant, Ann Smeets, Ines Nevelsteen, Rani Vanhoudt, Patrick Neven. Association between reproductive factors (parity and age first full term birth) and the frequency of estrogen receptor negative breast cancer according to age at diagnosis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-03-20.

Abstract PD17-08: Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials

Background: The Phase III MONALEESA (ML)-2, -3, and -7 trials showed significant improvement in progression-free survival (PFS) and overall survival (OS) with ribociclib (RIB) + endocrine therapy (ET) over placebo (PBO) + ET in patients (pts) with HR+/HER2− advanced breast cancer (ABC); improvement in OS with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) has been observed in some, but not all clinical trials. Gene expression analyses for each separate ML study were reported previously. Given the differences in CDK4 vs CDK6 inhibition between RIB and other CDK4/6i, we evaluated the association between cell cycle (CC)–related genes and outcomes based on pooled analysis of gene expression using tumor samples from the ML-2, -3, and -7 trials.

Methods: Gene expression data were generated from pre-treatment archival tumor samples (primary, 73%; metastatic, 27%) with a customized NanoString nCounter panel (781 genes) including genes involved in CC, other signaling pathways, and breast cancer biology. Samples were pooled from 1139 pre- and postmenopausal pts with HR+/HER2− ABC across the 3 ML studies, which included pts on first- and second-line therapy. Data were categorized into training (80%) and test (20%) datasets. The training dataset was used to analyze each gene (modeled continuously) individually for an association with PFS, and genes with a gene × treatment (tx) interaction P value &lt;.10 were evaluated in the test dataset. Genes or gene signatures were classified by tertiles based on expression level (low/medium/high). For each tertile, median (m) PFS was calculated by the Kaplan-Meier method, and hazard ratios (HRs) of tx benefit (RIB vs PBO) were estimated. A Cox proportional hazards model adjusting for clinical covariates was used. A machine learning approach (elastic net survival model with stability selection), which used available gene expression data and select clinical factors and their interactions with tx arms, was applied to predict PFS.

Results: This report focused on CC-related genes and signatures. Gene expression levels of CDKN2B and the expression ratio of CCND1/CDKN2A showed a predictive relationship with benefit from RIB in both training and test sets (Table). PFS benefit with RIB was consistent regardless of the CDK4/CDK6 expression ratio or level of expression of CCNE1, CDK2, RB1, combined CC-related genes, E2F gene signatures, RB gene signature, combined DNA-replication genes, or combined proliferation-related genes. A machine learning approach identified a clinico-genomic signature that was prognostic for PFS benefit with RIB. Selected variables included gene expression levels of FXBO5, PGR, RBBP8, and STC2 and several clinical features (tx arm, de novo disease, prior ET, and visceral disease). Pts with a low signature score had a longer mPFS vs pts with a high signature score, in the RIB (HR, 0.37; 95% CI, 0.22-0.62) and PBO (HR, 0.30; 95% CI, 0.15-0.59) arms.

Conclusion: In the largest pooled analysis of the association of gene expression profile data with CDK4/6i tx response in pts with HR+/HER2− ABC, the PFS benefit with RIB + ET over ET alone was consistent irrespective of expression levels of most CC genes. Variation in magnitude of RIB benefit was observed, depending on CDKN2B expression levels, CCND1/CDKN2A expression ratio, and machine learning–derived signature scores. The clinico-genomic CDK4/6i signature requires validation in additional datasets.

Table 1: Progression-Free Survival by Gene Expression Subgroup

Citation Format: Aditya Bardia, Faye Su, Nadia Solovieff, Fabrice Andre, Carlos Arteaga, Patrick Neven, Yoon-Sim Yap, Yen-Shen Lu, Stephen K. Chia, Dennis Slamon, Seock-Ah Im, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Debu Tripathy. Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD17-08.

Abstract P4-09-12: Baseline and End-of-Treatment Biomarkers in Patients With PIK3CA-Mutated, Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer From BYLieve Study Cohorts A and B

Introduction: Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) is mutated in ~40% of patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) advanced breast cancer (ABC). PIK3CA mutations are associated with resistance to endocrine therapy (ET) and worse overall survival. Alpelisib (ALP), an α-selective PI3K inhibitor and degrader, is indicated in combination with fulvestrant (FUL) for pts with PIK3CA-mutated (mut) HR+, HER2− ABC following progression on/after ET-based treatments. In the Phase 2, open-label, 3-cohort, noncomparative BYLieve study, clinical benefit of ALP in combination with ET was observed in the post-cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) setting in pts with PIK3CA-mut, HR+, HER2− ABC. Here we report the results of a biomarker analysis using paired baseline (Cycle 1 Day 1) and end-of-treatment (EOT) circulating tumor DNA (ctDNA) samples from pts in BYLieve Cohorts A and B.

Methods: In the BYLieve study, pts with PIK3CA-mut, HR+, HER2− ABC had CDK4/6i + aromatase inhibitor (Cohort A; N=127) or CDK4/6i + FUL (Cohort B; N=126) as treatment immediately prior to receiving ALP + FUL and ALP + letrozole, respectively. In this biomarker analysis, gene alterations were detected in ctDNA at baseline and EOT using next-generation sequencing (PanCancer V2 panel). Pts included in this interim analysis had confirmed PIK3CA mutations and matched baseline/EOT samples with enough sequencing coverage and ctDNA fraction to detect mutations at both time points. ctDNA fractions, tumor mutation burden (TMB) distributions, genomic landscapes, gain/loss of PIK3CA and estrogen receptor 1 (ESR1), chromosome 8/11 amplification profiles, and alterations in PI3K pathway and potential CDK4/6i resistance markers were assessed across time points. Sample sizes were small; results should thus be interpreted with caution.

Results: Forty-three pts were included in the Cohort A biomarker population and 40 pts were included in Cohort B. ctDNA fraction was numerically higher at EOT compared with baseline in both cohorts; further analyses will be presented. In Cohort A, no significant differences were observed in TMB at EOT compared with baseline (P=0.21). In Cohort B, TMB was higher at EOT compared with baseline (P=0.053). Chromosome 8/11 amplifications were consistent between baseline and EOT for both cohorts. Small variations were observed in ESR1/PIK3CA mutations between baseline and EOT on both cohorts (Table). The status of potential CDK4/6i resistance markers was relatively unchanged at EOT (Table). Loss-of-function mutations in PTEN, a known PI3K inhibitor resistance marker, increased from 9% at baseline to 14% at EOT in Cohort A and from 12% at baseline to 22% at EOT in Cohort B.

Conclusions: Between baseline and EOT, only small variations in gene alterations in PIK3CA-mutated HR+, HER2– ABC were observed in the post-CDK4/6i setting. As the disease progressed, increases in loss-of-function mutations in PTEN at EOT in both Cohorts A and B suggested loss of PTEN in PI3K pathway may drive resistance to ALP. Early intervention with ALP, when the tumor is particularly driven by PIK3CA oncogenic mutations and before it develops more genomic complexity, may potentially provide better clinical outcomes.

Table. Gene Alteration Gain/Loss at Baseline/EOT Across Cohorts A and B

Citation Format: Dejan Juric, Nicholas Turner, Sherene Loi, Fabrice Andre, Stephen K. Chia, Komal Jhaveri, Patrick Neven, Rebecca Dent, Eva Ciruelos, Mukta Joshi, Estelle Roux, Heather Patino, Murat Akdere, Hope Rugo. Baseline and End-of-Treatment Biomarkers in Patients With PIK3CA-Mutated, Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer From BYLieve Study Cohorts A and B [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-09-12.

Abstract P4-01-29: Ribociclib plus letrozole alters the immune subset composition in older (≥70 yrs.) patients with HR+/HER2- metastatic breast cancer

Background The combination of CDK4/6 inhibitors and endocrine therapy is the current standard first-line therapy for patients with HR+/HER2- metastatic breast cancer (mBC). Preliminary data suggest that CDK4/6 inhibitors not only induce tumor response by blocking CDK-dependent cell growth but that they can also alter the host immune function and stimulate tumor cell-directed immunity. However, clinical data are scarce, and no data exist about the impact of age and frailty, which are known to impact host immunity (immunosenescence). Materials and methods This prospective ongoing study is evaluating the efficacy and toxicity of the CDK4/6 inhibitor ribociclib and letrozole in older (≥ 70 years) patients with HR+/HER2- mBC (RIBOB, NCT03956654). In the associated blood biomarker sub-study, we investigate the impact of ribociclib and letrozole on the immune subset composition. Immune cell subsets were analyzed using flowcytometry (BD FACSVerse™) of peripheral blood mononuclear cells isolated at baseline (before ribociclib administration) and after three months of ribociclib treatment. In total, six multicolor flow cytometry staining panels were set up to investigate the changes in the immune cell subsets (CD4+ T-cell subsets, CD8+ T-cell subsets, general immune cell subsets, T-regulatory cell subsets, T-cell activation status subsets, and myeloid-derived suppressor cells subsets). Frailty status was assessed at baseline using the G8 screening tool (range score: 0-17) as a proxy. The paired t-test and matched-pairs Wilcoxon signed-rank test are used to evaluate changes in immune subset composition between baseline and after three months. The unpaired t-test and Mann-Whitney U test are used to evaluate differences in immune subset composition between frail and fit patients. Results Immune cell subset distribution and evolution were available for 15 older patients (median age: 77 yrs.; IQR 74-83), 4 considered fit (G8-score &gt;14), and 11 frail (G8-score ≤14). Firstly, we analyzed the difference in immune subset composition between baseline and three months for the whole cohort. There was a significant increase of naïve T-regulatory cells (p=0.0012) and a significant increase in CD8+ T-cell activation indicated by an upregulation of HLA-DR+ (p=0.0055) and CD38+ (p=0.0203). Secondly, the difference in immune subset composition between fit and frail persons was assessed showing a lower activation status of CD4+ and CD8+ T-cell subsets in frail persons at baseline, as assessed by several activation markers: CD4+PD1+ (p=0.0051), CD4+PD1+CD69+ (p=0.0013), CD8+PD1+ (p=0.0073), and CD8+PD1+CD69+ (p=0.0339). These significant differences between fit and frail disappeared after three months, largely because of increased T-cell activation in the frail subset. Conclusion Ribociclib plus letrozole treatment for three months results in an upregulation of the T-regulatory cells’ naïve subset, suggesting an expansion of the T-cell repertoire, which is compatible with immune cell activation. Furthermore, the activation status of the CD8+ T-cells was upregulated. These observations confirm recent findings reported by Scirocchi F. et al. (Lancet, 2022). In addition, frail older patients show a lower baseline T-cell activation status compared to fit older patients but seem to have increased T-cell activation after treatment exposure. In the future, correlations with treatment response will be evaluated when follow-up data matures. Our data encourage the further assessment of immune cell modulation in combination with CDK4/6 inhibitors in the treatment of patients with metastatic breast cancer.

Citation Format: Yentl Lambrechts, Sigrid Hatse, Cindy Kenis, Lore Decoster, Evandro de Azambuja, Guy Jerusalem, Patrick Neven, Lissandra Dal Lago, Hannelore Denys, Peter Vuylsteke, Frank Cornelis, Kevin Punie, Giuseppe Floris, Christine Desmedt, Annouschka Laenen, Noam Pondé, Hans Wildiers. Ribociclib plus letrozole alters the immune subset composition in older (≥70 yrs.) patients with HR+/HER2- metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-29.