Novel oral selective estrogen receptor degraders (SERDs) to target hormone receptor positive breast cancer: Elacestrant as the poster-child

INTRODUCTION

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer subtype, and therapeutic management relies primarily on inhibiting ER signaling. In the metastatic setting, ER signaling is typically targeted by selective estrogen receptor degraders (SERDs) or aromatase inhibitors (AIs), the latter of which prevent estrogen production. Activating ESR1 mutations are among the most common emergent breast cancer mutations and confer resistance to AIs.

AREAS COVERED

Until 2023, fulvestrant was the only approved SERD; fulvestrant is administered intramuscularly, and in some cases may also have limited efficacy in the setting of certain ESR1 mutations. In 2023, the first oral SERD, elacestrant, was approved for use in ESR1-mutated, ER+/HER2- advanced breast cancer and represents a new class of therapeutic options. While the initial approval was as monotherapy, ongoing studies are evaluating elacestrant (as well as other oral SERDs) in combination with other therapies including CDK4/6 inhibitors and PI3K inhibitors, which parallels the current combination uses of fulvestrant.

EXPERT OPINION

Elacestrant's recent approval sheds light on the use of biomarkers such as ESR1 to gauge a tumor's endocrine sensitivity. Ongoing therapeutic and correlative biomarker studies will offer new insight and expanding treatment options for patients with advanced breast cancer.

Response-guided neoadjuvant sacituzumab govitecan for localized triple-negative breast cancer: results from the NeoSTAR trial

BACKGROUND

Sacituzumab govitecan (SG), a novel antibody-drug conjugate (ADC) targeting TROP2, is approved for pre-treated metastatic triple-negative breast cancer (mTNBC). We conducted an investigator-initiated clinical trial evaluating neoadjuvant (NA) SG (NCT04230109), and report primary results.

PATIENTS AND METHODS

Participants with early-stage TNBC received NA SG for four cycles. The primary objective was to assess pathological complete response (pCR) rate in breast and lymph nodes (ypT0/isN0) to SG. Secondary objectives included overall response rate (ORR), safety, event-free survival (EFS), and predictive biomarkers. A response-guided approach was utilized, and subsequent systemic therapy decisions were at the discretion of the treating physician.

RESULTS

From July 2020 to August 2021, 50 participants were enrolled (median age = 48.5 years; 13 clinical stage I disease, 26 stage II, 11 stage III). Forty-nine (98%) completed four cycles of SG. Overall, the pCR rate with SG alone was 30% [n = 15, 95% confidence interval (CI) 18% to 45%]. The ORR per RECIST V1.1 after SG alone was 64% (n = 32/50, 95% CI 77% to 98%). Higher Ki-67 and tumor-infiltrating lymphocytes (TILs) were predictive of pCR to SG (P = 0.007 for Ki-67 and 0.002 for TILs), while baseline TROP2 expression was not (P = 0.440). Common adverse events were nausea (82%), fatigue (76%), alopecia (76%), neutropenia (44%), and rash (48%). With a median follow-up time of 18.9 months (95% CI 16.3-21.9 months), the 2-year EFS for all participants was 95%. Among participants with a pCR with SG (n = 15), the 2-year EFS was 100%.

CONCLUSIONS

In the first NA trial with an ADC in localized TNBC, SG demonstrated single-agent efficacy and feasibility of response-guided escalation/de-escalation. Further research on optimal duration of SG as well as NA combination strategies, including immunotherapy, are needed.

Axillary Nodal Response to Neoadjuvant T-DM1 Combined with Pertuzumab in a Prospective Phase II Multi-Institution Clinical Trial

BACKGROUND

Patients with ERBB2 (HER2)-positive breast cancer experience high pathologic complete response (pCR) rates after standard neoadjuvant anti-HER2 systemic therapy. We examined axillary pathologic nodal response to neoadjuvant dual HER2-targeted therapy alone, based on breast pathologic response, in a multi-institution clinical trial.

STUDY DESIGN

Patients with HER2-positive breast cancer were enrolled to a phase II single-arm trial, which administered 6 cycles of neoadjuvant trastuzumab emtansine (T-DM1) plus pertuzumab. Rates of pathologic nodal disease (ypN) in patients who were clinically node-negative (cN0) and node-positive (cN1) were analyzed, by residual breast disease (pCR and residual cancer burden [RCB] I to III).

RESULTS

One hundred fifty-eight patients completed preoperative treatment and proceeded to surgery. Of 92 patients who were cN0, 48 (52.2%) and 10 (10.9%) experienced breast pCR and RCB I, respectively. Of these, 100% were ypN0. Of 34 with RCB II to III, 26 (76.5%) were ypN0. Of 30 patients who were cN1 with breast pCR, 100% were ypN0; of the 12 patients who were cN1 with RCB I, 66.7% were ypN0; and of the 24 patients who were cN1 with RCB II to III, 25% were ypN0. ypN0 rates were significantly different between patients who did and did not experience a pCR, in both cN0 (p = 0.002) and cN1 (p < 0.001) subgroups.

CONCLUSIONS

Patients with HER2-positive breast cancer treated with dual HER2-targeted therapy who experienced a breast pCR or RCB I response were frequently ypN0. These findings support future trials considering omission of axillary surgical staging for patients with HER2-positive breast cancer in neoadjuvant trials of active HER2-targeted regimens, particularly if they experience breast pCR or RCB I.

Allosteric PI3Kα Inhibition Overcomes On-target Resistance to Orthosteric Inhibitors Mediated by Secondary PIK3CA Mutations

PIK3CA mutations occur in ∼8% of cancers, including ∼40% of HR-positive breast cancers, where the PI3K-alpha (PI3Kα)-selective inhibitor alpelisib is FDA approved in combination with fulvestrant. Although prior studies have identified resistance mechanisms, such as PTEN loss, clinically acquired resistance to PI3Kα inhibitors remains poorly understood. Through serial liquid biopsies and rapid autopsies in 39 patients with advanced breast cancer developing acquired resistance to PI3Kα inhibitors, we observe that 50% of patients acquire genomic alterations within the PI3K pathway, including PTEN loss and activating AKT1 mutations. Notably, although secondary PIK3CA mutations were previously reported to increase sensitivity to PI3Kα inhibitors, we identified emergent secondary resistance mutations in PIK3CA that alter the inhibitor binding pocket. Some mutations had differential effects on PI3Kα-selective versus pan-PI3K inhibitors, but resistance induced by all mutations could be overcome by the novel allosteric pan-mutant-selective PI3Kα-inhibitor RLY-2608. Together, these findings provide insights to guide strategies to overcome resistance in PIK3CA-mutated cancers.

SIGNIFICANCE

In one of the largest patient cohorts analyzed to date, this study defines the clinical landscape of acquired resistance to PI3Kα inhibitors. Genomic alterations within the PI3K pathway represent a major mode of resistance and identify a novel class of secondary PIK3CA resistance mutations that can be overcome by an allosteric PI3Kα inhibitor. See related commentary by Gong and Vanhaesebroeck, p. 204 . See related article by Varkaris et al., p. 240 . This article is featured in Selected Articles from This Issue, p. 201.

HER2 heterogeneity and treatment response-associated profiles in HER2-positive breast cancer in the NCT02326974 clinical trial

BACKGROUNDHER2-targeting therapies have great efficacy in HER2-positive breast cancer, but resistance, in part due to HER2 heterogeneity (HET), is a significant clinical challenge. We previously described that in a phase II neoadjuvant trastuzumab emtansine (T-DM1) and pertuzumab (P) clinical trial in early-stage HER2-positive breast cancer, none of the patients with HER2-HET tumors had pathologic complete response (pCR).METHODSTo investigate cellular and molecular differences among tumors according to HER2 heterogeneity and pCR, we performed RNA sequencing and ERBB2 FISH of 285 pretreatment and posttreatment tumors from 129 patients in this T-DM1+P neoadjuvant trial. A subset of cases was also subject to NanoString spatial digital profiling.RESULTSPretreatment tumors from patients with pCR had the highest level of ERBB2 mRNA and ERBB signaling. HER2 heterogeneity was associated with no pCR, basal-like features, and low ERBB2 expression yet high ERBB signaling sustained by activation of downstream pathway components. Residual tumors showed decreased HER2 protein levels and ERBB2 copy number heterogeneity and increased PI3K pathway enrichment and luminal features. HET tumors showed minimal treatment-induced transcriptomic changes compared with non-HET tumors. Immune infiltration correlated with pCR and HER2-HET status.CONCLUSIONResistance mechanisms in HET and non-HET tumors are distinct. HER2-targeting antibodies have limited efficacy in HET tumors. Our results support the stratification of patients based on HET status and the use of agents that target downstream components of the ERBB signaling pathway in patients with HET tumors.TRIAL REGISTRATIONClinicalTrials.gov NCT02326974.FUNDINGThis study was funded by Roche and the National Cancer Institute.

Virtual Molecular and Precision Medicine Clinic to Improve Access to Clinical Trials for Patients With Metastatic Breast Cancer: An Academic/Community Collaboration

PURPOSE

There is a demand for improved care delivery surrounding genomic testing and clinical trial enrollment among patients with metastatic breast cancer (MBC). We sought to improve the current process via real-time informal consultation and prescreening assessment for patients with MBC treated by community and academic medical oncologists by implementing a virtual molecular and precision medicine (vMAP) clinic.

METHODS

The vMAP program used a virtual referral system directed to a multidisciplinary team with precision medicine expertise. Providers contacted vMAP regarding patients with MBC, and on receipt of referral, the vMAP team engaged in discussion to identify if further diagnostics were needed (including genomic testing) and to identify potential clinical trials or standard treatment options. Recommendations were then sent to the referring provider within 72 hours. Pre-/postsurveys were issued to network physicians to assess for barriers, clinical trial access, and vMAP referral experience. Program implementation was evaluated with the Squire 2.0 reporting guidelines for quality improvement in health care as a framework.

RESULTS

Eighty-one cases from 22 providers were referred to vMAP over a 26-month period. The average response time to the referring provider with a finalized recommendation was 1.90 ± 1.82 days. A total of 86.4% of cases had clinical trial options on vMAP prescreen, with 40.7% initiating formal screening assessments and 27 patients (33.3%) ultimately enrolling on trials. On resurvey, 92% of survey responses across community oncology referring providers said that they were very likely to use vMAP again.

CONCLUSION

In the initial 2-year period, vMAP demonstrated an efficient means to offer real-time interpretation of genomic testing and identification of clinical trials for patients with MBC, with effective clinical trial enrollment and high rates of referring provider satisfaction.

Ultrasensitive Detection of Circulating LINE-1 ORF1p as a Specific Multicancer Biomarker

Improved biomarkers are needed for early cancer detection, risk stratification, treatment selection, and monitoring treatment response. Although proteins can be useful blood-based biomarkers, many have limited sensitivity or specificity for these applications. Long INterspersed Element-1 (LINE-1) open reading frame 1 protein (ORF1p) is a transposable element protein overexpressed in carcinomas and high-risk precursors during carcinogenesis with negligible expression in normal tissues, suggesting ORF1p could be a highly specific cancer biomarker. To explore ORF1p as a blood-based biomarker, we engineered ultrasensitive digital immunoassays that detect mid-attomolar (10-17 mol/L) ORF1p concentrations in plasma across multiple cancers with high specificity. Plasma ORF1p shows promise for early detection of ovarian cancer, improves diagnostic performance in a multianalyte panel, provides early therapeutic response monitoring in gastroesophageal cancers, and is prognostic for overall survival in gastroesophageal and colorectal cancers. Together, these observations nominate ORF1p as a multicancer biomarker with potential utility for disease detection and monitoring.

SIGNIFICANCE

The LINE-1 ORF1p transposon protein is pervasively expressed in many cancers and is a highly specific biomarker of multiple common, lethal carcinomas and their high-risk precursors in tissue and blood. Ultrasensitive ORF1p assays from as little as 25 μL plasma are novel, rapid, cost-effective tools in cancer detection and monitoring. See related commentary by Doucet and Cristofari, p. 2502. This article is featured in Selected Articles from This Issue, p. 2489.

Molecular Residual Disease in Breast Cancer: Detection and Therapeutic Interception

Breast cancer remains a leading cause of cancer-related death in women despite screening and therapeutic advances. Early detection allows for resection of local disease; however, patients can develop metastatic recurrences years after curative treatment. There is no reliable blood-based monitoring after curative therapy, and radiographic evaluation for metastatic disease is performed only in response to symptoms. Advances in circulating tumor DNA (ctDNA) assays have allowed for a potential option for blood-based monitoring. The detection of ctDNA in the absence of overt metastasis or recurrent disease indicates molecular evidence of cancer, defined as molecular residual disease (MRD). Multiple studies have shown that MRD detection is strongly associated with disease recurrence, with a lead time prior to clinical evidence of recurrence of many months. Importantly, it is still unclear whether treatment changes in response to ctDNA detection will improve outcomes. There are currently ongoing trials evaluating the efficacy of therapy escalation in the setting of MRD, and these studies are being conducted in all major breast cancer subtypes. Additional therapies under study include CDK4/6 inhibitors, PARP inhibitors, HER2-targeted therapies, and immunotherapy. This review will summarize the underlying scientific principles of various MRD assays, their known prognostic roles in early breast cancer, and the ongoing clinical trials assessing the efficacy of therapy escalation in the setting of MRD.

Endocrine Therapy for Surgeons: Practical Pearls for Managing Menopausal, Bone Loss and Sexual Adverse Effects

Breast cancer patients are living longer than ever before and as such the population of breast cancer survivors continues to grow. Approximately 80% of breast cancers are hormone receptor-positive (HR+) and most patients will receive neoadjuvant or adjuvant estrogen blockade, referred to as endocrine therapy. Although endocrine therapy reduces HR+ breast cancer recurrence by 30-50%, significant adverse effects pose a threat to treatment adherence. These adverse effects include vasomotor symptoms, colloquially referred to as hot flashes, bone loss, joint arthralgias, genitourinary syndrome of menopause (GSM), previously referred to as vaginal atrophy, and low libido. This review will present the evidence-based treatments available for each of these adverse effects, including clear treatment algorithms for GSM, which is often experienced by patients but overlooked by providers. The most important takeaway is to ask open-ended questions, encourage reporting of these symptoms, and refer patients to specialty providers as needed. Surgeons may be the first to encounter these symptoms, therefore it is critical to remain informed of the treatment options.

Impact of Neoadjuvant Paclitaxel/Trastuzumab/Pertuzumab on Breast Tumor Downsizing for Patients with HER2+ Breast Cancer: Single-Arm Prospective Clinical Trial

BACKGROUND

The impact of abbreviated neoadjuvant regimens for HER2+ breast cancer on rates of breast conservation therapy (BCT) is unclear. We aimed to determine BCT rates in a single-arm prospective trial of neoadjuvant paclitaxel/trastuzumab/pertuzumab (THP) in patients with stage II-III HER2+ breast cancer.

STUDY DESIGN

BCT eligibility was prospectively recorded before and after THP. Pre- and post-treatment mammogram and breast ultrasound were required; breast MRI was encouraged. Patients with a large tumor to breast size ratio were eligible for downsizing. Multifocal/multicentric tumors, extensive calcifications, and contraindications to radiation were considered BCT contraindications.

RESULTS

Overall, 92 patients who received neoadjuvant THP on trial were included. At presentation, 39 (42.4%) were considered eligible for BCT and 53 (57.6%) were not. BCT-eligible patients were older (median 54 years versus 47 years, respectively, p=0.006) and had smaller tumors by palpation (median 2.5 cm versus 3 cm, respectively, p=0.004). Of 53 BCT-ineligible patients, 28 were candidates for tumor downsizing, whereas 25 had contraindications to BCT. Overall, 51(55.4%) patients underwent BCT. Of the 28 patients who were candidates for downsizing, 22 (78.6%) became BCT-eligible after THP and 18/22 (81.8%) underwent BCT. In total, 44/92 (47.8%) patients experienced breast pathologic complete response (pCR, ypT0), including 11/25 (44.0%) patients with BCT contraindications at presentation.

CONCLUSIONS

De-escalated neoadjuvant systemic therapy led to high BCT rates in this cohort. The impact of de-escalated systemic therapy on local therapy and outcomes in early stage HER2+ breast cancer warrants further investigation.

A Gene Panel Associated With Abemaciclib Utility in ESR1-Mutated Breast Cancer After Prior Cyclin-Dependent Kinase 4/6-Inhibitor Progression

PURPOSE

For patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), first-line treatment is endocrine therapy (ET) plus cyclin-dependent kinase 4/6 inhibition (CDK4/6i). After disease progression, which often comes with ESR1 resistance mutations (ESR1-MUT), which therapies to use next and for which patients are open questions. An active area of exploration is treatment with further CDK4/6i, particularly abemaciclib, which has distinct pharmacokinetic and pharmacodynamic properties compared with the other approved CDK4/6 inhibitors, palbociclib and ribociclib. We investigated a gene panel to prognosticate abemaciclib susceptibility in patients with ESR1-MUT MBC after palbociclib progression.

METHODS

We examined a multicenter retrospective cohort of patients with ESR1-MUT MBC who received abemaciclib after disease progression on ET plus palbociclib. We generated a panel of CDK4/6i resistance genes and compared abemaciclib progression-free survival (PFS) in patients without versus with mutations in this panel (CDKi-R[-] v CDKi-R[+]). We studied how ESR1-MUT and CDKi-R mutations affect abemaciclib sensitivity of immortalized breast cancer cells and patient-derived circulating tumor cell lines in culture.

RESULTS

In ESR1-MUT MBC with disease progression on ET plus palbociclib, the median PFS was 7.0 months for CDKi-R(-) (n = 17) versus 3.5 months for CDKi-R(+) (n = 11), with a hazard ratio of 2.8 (P = .03). In vitro, CDKi-R alterations but not ESR1-MUT induced abemaciclib resistance in immortalized breast cancer cells and were associated with resistance in circulating tumor cells.

CONCLUSION

For ESR1-MUT MBC with resistance to ET and palbociclib, PFS on abemaciclib is longer for patients with CDKi-R(-) than CDKi-R(+). Although a small and retrospective data set, this is the first demonstration of a genomic panel associated with abemaciclib sensitivity in the postpalbociclib setting. Future directions include testing and improving this panel in additional data sets, to guide therapy selection for patients with HR+/HER2- MBC.

Feasibility of introducing a smartphone navigation application into the care of breast cancer patients (The FIONA Study)

PURPOSE

Patients with breast cancer (BC) face complex medical information and decisions. The Outcomes4Me mobile app provides evidence-based BC education, symptom management tracking and clinical trial matching. This study sought to evaluate the feasibility of introducing this app into routine BC care.

METHODS

In this pilot study among BC patients undergoing therapy at an academic cancer center, patients were followed for 12 weeks with survey administration and electronic health record (EHR) abstraction at baseline and completion. Feasibility was defined as 40% of patients engaging with the app 3 or more times during the study. Additional endpoints included app usability (system usability scale), patient care experience, symptom evaluation, and clinical trial matching.

RESULTS

The study enrolled 107 patients from 6/01/2020 to 3/31/2021. Utilization of the app was deemed feasible with 60% of patients engaging with the app at least 3 times. SUS score of 70 indicated above average usability. New diagnosis and higher education level was associated with greater app engagement, with usability similar across all age groups. 41% of patients found the app helped track symptoms. Cognitive and sexual symptoms were infrequently reported, but were more frequently captured in the app than in the EHR. After using the app, 33% of patients reported increased interest in clinical trial enrollment.

CONCLUSION

Introducing the Outcomes4Me patient navigation app into routine BC care is feasible and may improve the patient experience. These results support further evaluation of this mobile technology platform to improve BC education, symptom management, and decision making.

CLINICAL TRIAL REGISTRY

Clinicaltrials.gov registration #: NCT04262518.

Abstract 960: Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer

Background Antibody drug conjugates (ADC) are novel drugs linking potent payloads to antibodies targeting antigen-expressing tumors. Sacituzumab govitecan (SG), targeting Trop-2, is approved for metastatic triple negative breast cancer (TNBC); and trastuzumab deruxtecan, targeting HER2, is approved for HER2-positive and HER2-low metastatic breast cancer. To understand the potentially overlapping clinical landscape of Trop-2 and HER2 antigens, we evaluated RNA expression data in breast cancer from The Cancer Genome Atlas (TCGA) project.

Methods TCGA dataset was assessed for Trop-2 and HER2 expression via processed RNA sequencing (RNA-seq) data of the corresponding genes TACSTD2 and ERBB2. Medium/high gene expression was assessed as &gt;100 transcripts per million (TPM). Samples were classified HER2-low per ASCO/CAP guidelines. Gene expression across clinical parameters was assessed via one-way ANOVA.

Results 1076 patients with primary breast cancer were included. The majority (59%) had both high TACSTD2 expression (TACSTD2hi) and high ERBB2 expression (ERBB2hi) (see Table). Median TACSTD2 expression was 572 TPM (IQR 349-666 TPM); median ERBB2 expression was 122 TPM (IQR 73-192 TPM). No significant difference was observed in TACSTD2 or ERBB2 expression among invasive ductal carcinoma, invasive lobular carcinoma, mixed histology, or other (p = 0.07, 0.23). No significant difference in TACSTD2 expression was noted between HER2-low and HER2-negative subtypes (p=0.34).

Conclusions While SG is approved in TNBC, TACSTD2 is expressed across all breast cancer subtypes, including HER2-low, suggesting a broader population may benefit from Trop-2-targeted ADCs. Furthermore, given that over half of breast cancers have high expression of both TACSTD2 and ERBB2, additional studies are needed to understand the optimal sequencing of ADC-based therapies for patients with breast cancer.

Table Patient subsets(HR = hormone receptor) n TACSTD2hi & ERBB2hi TACSTD2hi & ERBB2low TACSTD2low & ERBB2hi TACSTD2low & ERBB2low All 1,076 632 (59%) 394 (36%) 19 (2%) 31 (3%) Histology 843 Invasive ductal carcinoma 507 267 (32%) 215 (25%) 10 (1%) 15 (2%) Invasive lobular carcinoma 130 103 (12%) 24 (3%) 1 (&lt;1%) 2 (&lt;1%) Mixed 91 63 (7%) 24 (3%) 2 (&lt;1%) 2 (&lt;1%) Other 115 65 (8%) 43 (5%) 2 (&lt;1%) 5 (&lt;1%) HER2 Status 345 HR+/HER2-low 254 170 (49%) 77 (22%) 6 (1%) 1 (&lt;1%) TNBC/HER2-low 55 12 (3%) 39 (11%) 1 (&lt;1%) 3 (&lt;1%) HR+/HER2-negative 24 13 (4%) 11 (3%) 0 0 TNBC/HER2-negative 12 1 (&lt;1%) 10 0 1 (&lt;1%)

Citation Format: Arielle J. Medford, Nicholas J. Haradhvala, Neelima Vidula, Rachel Abelman, Laura M. Spring, Leif W. Ellisen, Gad Getz, Aditya Bardia. Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 960.

Ultrasensitive detection of circulating LINE-1 ORF1p as a specific multi-cancer biomarker

Improved biomarkers are needed for early cancer detection, risk stratification, treatment selection, and monitoring treatment response. While proteins can be useful blood-based biomarkers, many have limited sensitivity or specificity for these applications. Long INterspersed Element-1 (LINE-1, L1) open reading frame 1 protein (ORF1p) is a transposable element protein overexpressed in carcinomas and high-risk precursors during carcinogenesis with negligible detectable expression in corresponding normal tissues, suggesting ORF1p could be a highly specific cancer biomarker. To explore the potential of ORF1p as a blood-based biomarker, we engineered ultrasensitive digital immunoassays that detect mid-attomolar (10-17 M) ORF1p concentrations in patient plasma samples across multiple cancers with high specificity. Plasma ORF1p shows promise for early detection of ovarian cancer, improves diagnostic performance in a multi-analyte panel, and provides early therapeutic response monitoring in gastric and esophageal cancers. Together, these observations nominate ORF1p as a multi-cancer biomarker with potential utility for disease detection and monitoring.

Abstract PD1-10: Impact of Race on Clinical, Socioeconomic, and Genomic Characteristics, Clinical Trial Participation, and Receipt of Genotype-matched Therapy Among Patients with Metastatic Breast Cancer

Background: Clinical outcomes in breast cancer differ across racial and ethnic populations. We have previously demonstrated that receipt of genotype-matched therapy targeted to an actionable mutation may potentially improve patient outcomes (Vidula, CCR, 2021). We evaluated the impact of race on clinical, socioeconomic, and genomic characteristics, clinical trial participation, and receipt of genotype-matched therapy among patients with metastatic breast cancer (MBC). Methods: We conducted a retrospective study of patients with MBC at an academic institution who underwent cell-free DNA testing (cfDNA, Guardant360, 74 gene panel) as part of routine clinical care from 11/29/2016-11/2/2020. Patient demographics (including self-reported race and ethnicity) and clinical trial enrollment (at same institution) were determined by retrospective data collection. Mutations identified in cfDNA were characterized as actionable based on the variant interpretation performed by Guardant360 using vetted genomic databases, and receipt of genotype-matched therapy targeted to an actionable mutation was determined as previously described (Vidula, CCR, 2021). Pearson’s chi-squared and Wilcoxon rank-sum tests were used to compare categorical and continuous variables between groups, with p&lt; 0.05 indicating statistical significance. Results: Four hundred and twenty-five patients with MBC and cfDNA results were identified, of which 369 were White (87%), 27 Black (6.4%), 15 Hispanic (3.5%), and 14 Asian (3.3%). There were no significant differences in median age at MBC diagnosis (p=0.064), disease subtype distribution (p=0.74), proportions of de-novo/recurrent MBC (p=0.95), presence of visceral metastases (p=0.84), Charleston comorbidity index (p=0.93), menopausal status (p=0.3), and level of education (p=0.44) across racial groups. Higher proportions of non-primary English speakers were seen in Hispanic (80%) and Asian (29%) races (p&lt; 0.001). Median distance traveled to the institution also varied based on race, with White patients traveling further (White: 39.1 miles, Black: 21.8 miles, Hispanic 9.4 miles, Asian 9.1 miles, p&lt; 0.001). In addition, type of insurance varied based on race, with White patients having the highest rates of commercial insurance and Medicare, Black patients having the highest rate of state-supported insurance, and Asian patients having the highest uninsured rates (p&lt; 0.001). Clinical trial enrollment rates did not significantly differ by race (White: 44%, Black: 37%, Hispanic: 47%, and Asian 21%, p=0.34), but patients without insurance were significantly less likely to be enrolled on a trial than those with commercial insurance (p=0.03). The proportion of patients with ≥1 actionable mutation in cfDNA did not vary significantly by race (White: 78%, Black: 56%, Hispanic: 73%, Asian 86%, p=0.18) and the median number of actionable mutations found in cfDNA was similar across races (p=0.31). However, receipt of genotype-matched therapy targeted to an actionable mutation varied by race, with the highest rates of matched therapy in White patients (White: 28%, Black: 11%, Hispanic 13%, Asian 14%, p&lt; 0.001). After multivariable logistic regression adjusting for subtype, commercial insurance versus other insurance types, and proximity to the center, White patients remained significantly more likely to receive matched therapy (p=0.029). Conclusions: We observed significant race-based differences in non-English speaking status, insurance type, and median distance traveled to the institution. Racial/ethnic minority patients were less likely to receive genotype-matched therapy than White patients. Further research is needed to identify barriers and reduce disparities in access to precision medicine.

Citation Format: Rupali Sood, Lianne Ryan, Andrzej Niemierko, Laura M. Spring, Dejan Juric, Steven J. Isakoff, Seth A. Wander, Jennifer Shin, Naomi Ko, Leif Ellisen, Beverly Moy, Aditya Bardia, Neelima Vidula. Impact of Race on Clinical, Socioeconomic, and Genomic Characteristics, Clinical Trial Participation, and Receipt of Genotype-matched Therapy Among 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 PD1-10.

Abstract PD13-07: PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial

Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) provide significant clinical benefit in patients with HR+/HER2- metastatic breast cancer (MBC) and have become a standard of care treatment. Prior insights from tumor profiling and preclinical analyses suggest that AKT1 activation can induce CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may be an effective therapeutic strategy and conducted a clinical trial to evaluate both doublet (ET+AKTi) and triplet (ET+AKTIi+CDK 4/6i) therapy in the ≥ 2nd line MBC setting. Methods: TAKTIC is an open-label phase Ib clinical trial (clinicaltrials.gov NCT03959891) evaluating the combination of the AKT inhibitor ipatasertib (ipat) with fulvestrant (Arm A), an aromatase inhibitor (Arm B), or the triplet combination (Arm C) with fulvestrant + palbociclib (palbo). The primary objective is to evaluate the safety (NCI CTCAE 5.0) and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Secondary objectives include clinical efficacy, as determined by objective response rate (RECIST v1.1), clinical benefit rate (CBR), progression-free survival (PFS), and overall survival (OS). Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an updated interim analysis from all study arms. Results: The trial completed accrual with 77 pts enrolled from June 2019 – February 2022, including 19 on Arm A, 16 on Arm B, and 42 on Arm C. Median age was 62 (range 32-88) and 65/77 pts (84%) received prior CDK4/6i (median no. of prior lines = 3, range 1-13). 56/77 pts (73%) had measurable disease at baseline and 50/77 pts (65%) had visceral metastases in the liver/lung (68% Arm A, 44% Arm B, 71% Arm C). Pts enrolled on Arms A and B received ipat at 400mg in combination with fulvestrant or an aromatase inhibitor, respectively. In Arm C, 27/42 pts enrolled into the dose escalation phase and received ipat + palbo at varying doses in combination with fulvestrant. Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days). ET+400mg ipat + 100mg palbo was determined to be the recommended phase 2 dose (R2PD), and the remaining 15/42 pts on Arm C were treated at this dose level in the expansion phase. Treatment was well tolerated in all arms. Grade 3 and 4 toxicities included neutropenia (39/77, 50.6%), leukopenia (15/77, 19.5%), diarrhea (11/77, 14/3%), transaminitis (7/77, 9.1%), lymphopenia (6/77, 7.8%), rash (6/77, 7.8%), and thrombocytopenia (3/77, 3.9%). As of 6/28/2022, 16/77 pts remain on treatment. The median treatment duration for all pts is estimated at 6 months (range 0.5-39). Among the 56 pts with measurable disease, 11 had partial response (PR) and 32 had stable disease (SD) as the best response. CBR, defined as percentage of pts who achieved PR or SD &gt; 6 months, was 48% across the study (53% Arm A, 31% Arm B, 57% Arm C). The median PFS was 5.5 months (95% confidence interval [CI]: 3.8 – 7.4) and the median OS was 24.5 months (95% CI: 17.1 – 33.9). Conclusions: The combination of ipat with endocrine therapy +/- palbo is well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. This trial demonstrates how molecular insights related to CDK4/6i resistance inform potential therapy combinations. Further studies are needed to evaluate AKTi-based combinations in pts with HR+ MBC.

Citation Format: Seth A. Wander, Jennifer C. Keenan, Andrzej Niemierko, Dejan Juric, Laura M. Spring, Jeffrey Supko, Neelima Vidula, Steven J. Isakoff, Lianne Ryan, Sarah Padden, Elizabeth Fisher, Amber Newton, Beverly Moy, Leif Ellisen, Douglas S. Micalizzi, Aditya Bardia. PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial [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 PD13-07.

Abstract OT3-25-01: Neoadjuvant HER2-targeted Therapy +/- Immunotherapy with Pembrolizumab (neoHIP): An Open Label Randomized Phase II Trial

Background: Immune checkpoint inhibition (ICI) is synergistic with HER2-directed therapy in pre-clinical models. Clinically, pembrolizumab (K)-mediated ICI plus HER2-directed therapy with trastuzumab (H) was safe and demonstrated modest activity in H-resistant HER2-positive (HER2+) metastatic breast cancer. Because ICI may confer more robust activity when administered earlier in the course of disease, H and K administered in the curative-intent, treatment-naive setting may allow for de-escalation of cytotoxic chemotherapy; confer life-long, tumor-specific immunity; and ultimately, improve cure rates. Moreover, the synergy of H and K with paclitaxel (T) may overcome the need for dual HER2-blockade with H plus pertuzumab (P). In this randomized, multicenter, phase II, open-label, multi-center trial the efficacy and safety of neoadjuvant THP vs THP-K vs TH-K are explored. Methods: 174 patients (pts) ≥18y with previously untreated, stage II-III, HER2+ breast cancer will be randomized and stratified by clinical nodal status (positive vs. negative) and hormone receptor status (positive vs. negative). In arm A, pts receive T at 80mg/m2 weekly for 12 weeks, H at 8mg/Kg (loading dose) and then 6mg/Kg every 3 weeks x 3 doses, P at 840 mg (loading dose) and then 420mg/Kg every 3 weeks x 3 doses (THP). In arm B, pts receive THP plus K at 200mg every 3 weeks x 4 doses (THP-K). In arm C, pts receive TH-K; however, in a preplanned interim analysis, arm C did not meet the pre-defined efficacy threshold and this arm was subsequently closed. Enrollment to arms A and B continue. Definitive surgery is 3-6 weeks after the last dose. After surgery, pts are treated per the treating physician’s discretion including radiotherapy per local clinical standard. Pts whose tumors are hormone-receptor positive will receive hormone therapy per local standard-of-care. The primary end point is pathologic complete response (pCR) rate in the breast and axilla (ypT0/Tis ypN0). Secondary end points include pCR rate by ypT0ypN0 and ypT0/Tis, residual cancer burden index, event free survival, breast conserving surgery rate, safety and overall survival. Exploratory correlative studies will characterize potential immune biomarkers predictive of efficacy and/or toxicity. Funding sources: BCRF, Merck NCT03747120

Citation Format: Heather McArthur, Jorge Henrique Santos Leal, Christina DiLauro Abaya, Sangeetha Reddy, Meredith Carter, Reva Basho, Michelle Phillips, David Chan, Hugo Hool, Dorothy Park, Mary El-Masry, Philomena McAndrew, Swati Sikaria, Laura M. Spring, Aditya Bardia, Mourad Tighiouart, Farnaz Dadmanesh, Armando Giuliano, Stephen Shiao, David B. Page. Neoadjuvant HER2-targeted Therapy +/- Immunotherapy with Pembrolizumab (neoHIP): An Open Label Randomized Phase II Trial [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 OT3-25-01.

Abstract P5-02-13: TRK inhibitor in a patient with metastatic triple negative breast cancer and NTRK fusions identified via cell-free DNA analysis

Introduction: Tissue-agnostic indications for targeted therapies are expanding options for patients with advanced solid tumors. The FDA approvals of the PD-1 inhibitor pembrolizumab and the TRK inhibitors larotrectinib and entrectinib provide rationale for next generation sequencing (NGS) in effectively all advanced solid tumor patients, as findings may indicate targeted therapy even in disease that may seem otherwise refractory. Here, we present the case of a post-menopausal woman with metastatic triple negative breast cancer (TNBC) who had disease progression on multiple lines of therapy prior to the identification of two actionable NTRK mutations, identified via cell-free DNA (cfDNA) and tissue-based NGS. She was subsequently started on the TRK inhibitor larotrectinib and had a marked clinical response. Case Presentation: A 64-year-old woman presented with metastatic TNBC five years after being treated for a localized breast cancer. The cancer rapidly progressed through 4 lines of therapy in the metastatic setting, including immunotherapy [atezolizumab/nab-paclitaxel (progression after 5 months)], antibody-drug conjugate-based therapy [sacituzumab govitecan (progression after 2 months)], and chemotherapy [gemcitabine/carboplatin (progression after 3 months), eribulin (progression after 2 months)]. Her CA 15-3 had also been consistently increasing to a peak of 206 IU/mL. Germline genetic testing was negative. Ultimately, NGS evaluation of cfDNA via an 83-gene assay (Guardant Health, Inc.) identified two NTRK3 fusions: an ETV6-NTRK3 fusion [mutant allele fraction (MAF) = 10.9%] associated with the rare secretory breast carcinoma, and CRTC3-NTRK3 (MAF = 3.2%), a fusion partner previously undescribed in breast cancer. Liver biopsy was sent for whole exome sequencing and RNA-seq analysis (BostonGene, Inc), which provided orthogonal confirmation of both the ETV6-NTRK3 and CRTC3-NTRK3 fusions. Review of the tumor pathology showed invasive ductal carcinoma with secretory features; this pathology and the ETV6-NTRK3 fusion were consistent with a diagnosis of secretory breast carcinoma. She was started on the TRK inhibitor larotrectinib, and she had a significant clinical and radiographic response after only two months of therapy. Recheck of her CA 15-3 showed a decrease to 48 IU/mL, the lowest level in our records. Repeat cfDNA testing showed a decrease of the ETV6-NTRK3 fusion to MAF 0.40% and the CRTC3-NTRK3 fusion to MAF 0.07%. The patient took larotrectinib for 7 months with good disease control. Unfortunately, unrelated to her therapy, she had experienced multiple fractures secondary to her existing osseous metastases, and these led to significant morbidity. She and her family elected to transition to comfort measures, after which she passed away. Discussion: In the presented case, the identification of NTRK fusions by plasma-based genotyping resulted in matched selection of genotype-directed therapy, and this otherwise refractory TNBC exhibited marked response to targeted therapy. While TNBC had historically been considered a subtype of breast cancer without targetable options, the expanding roles of NGS testing and targeted therapies are changing the paradigm. The actionability of rare genomic events such as NTRK fusions makes identifying them critical for individual patients, particularly in heterogeneous diseases such as TNBC. Tissue-agnostic targeted therapies now give reason for NGS testing in most solid tumors, as reflected in updated consensus guidelines. This case demonstrates the significant potential benefits of NGS testing in advanced and refractory cancers.

Citation Format: Jennifer C. Keenan, Arielle J. Medford, Lauren J. Oshry, Baris Boyraz, Charles S. Dai, Lesli A. Kiedrowski, Sofia Menshikova, Anna Butusova, Tasos Gogakos, Rachel Occhiogrosso, Phoebe Ryan, Jochen Lennerz, Laura M. Spring, Beverly Moy, Leif Ellisen, Aditya Bardia. TRK inhibitor in a patient with metastatic triple negative breast cancer and NTRK fusions identified via cell-free DNA analysis. [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 P5-02-13.

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 PD17-03: Cell-free DNA monitoring in a phase II study of adjuvant endocrine therapy with CDK 4/6 inhibitor ribociclib for localized HR+/HER2- breast cancer (LEADER)

Background: While adjuvant endocrine therapy (ET) reduces recurrence risk in hormone receptor-positive (HR+) breast cancer, many patients still experience disease recurrence. Adjuvant therapeutic advances are needed to improve outcomes. Meanwhile, monitoring for circulating tumor DNA (ctDNA) in the adjuvant setting may detect molecular residual disease and/or emergences of molecular recurrence from tumor dormancy. Cyclin-dependent kinase 4 and 6 (CDK 4/6) inhibitors have shown efficacy in HR+/HER2- metastatic breast cancer, and abemaciclib is now approved for adjuvant use in high-risk HR+/HER2- breast cancer. Adjuvant clinical trials have evaluated upfront use of adjuvant CDK 4/6 inhibition; however, the optimal timing of adding a CDK 4/6 inhibitor for HR+/HER2- breast cancer remains unknown. We conducted a prospective phase II clinical trial to evaluate the addition of the CDK 4/6 inhibitor ribociclib in patients with at least one remaining year of adjuvant ET regardless of duration of ET prior to trial enrollment, and we prospectively collected plasma for ctDNA analysis. Methods: Eligible patients had Stage I-III HR+/HER2- breast cancer and had been on adjuvant ET (any number of years) with at least one year of treatment remaining. Patients were randomized to one of two ribociclib schedules: continuous (400 mg daily, 28-day cycle) or intermittent (600 mg daily days 1-21, 28-day cycle) for one year. Patients were concurrently treated with an aromatase inhibitor (plus GnRH agonist, if premenopausal). Time to recurrence was calculated using the Kaplan-Meier method. ctDNA monitoring was performed using the SignateraTM platform, a tumor-informed assay based on whole exome sequencing of the primary tumor for multiplex PCR-NGS ctDNA assay design with targeting of up to 16 single nucleotide variants. Plasma samples were collected at the start of ribociclib/ET and serially during follow-up visits. Results: Among 81 patients treated with adjuvant endocrine therapy and the CDK4/6 inhibitor ribociclib, 42 patients had samples suitable for ctDNA analysis: 3 (7%) had a single ctDNA test, 17 (40%) had 2 serial ctDNA tests, and 22 (52%) had 3 serial ctDNA tests. After a median follow-up of 20 months, 2 patients who received ribociclib (intermittent dosing) experienced disease recurrence with recurrence-free survival of 100% at 1 year from study entry and 97% (95% CI 88-99%) at 2 years. ctDNA was detected exclusively in the only 2 patients that experienced recurrence, with lead times of 7 months and 8 months prior to clinical recurrence. Both patients had no detectable ctDNA at the start of ribociclib/ET. One patient had detectable ctDNA [mean tumor molecules/mL (MTM/mL) = 0.1] while on ribociclib/ET for 5 months, after which she completed a full 12 months of treatment. One month after completing ribociclib/ET (8 months after ctDNA detection), she presented with metastases in the liver and bones. The second patient had 2 negative ctDNA tests at days 0 and 147 while receiving ribociclib/ET and became ctDNA positive (MTM/mL = 0.1) at day 350. She developed CNS-only metastatic disease 7 months after completing ribociclib/ET. Among the other 40 patients who did not have detectable ctDNA, none have experienced recurrence. Conclusions: Overall, only 2 patients had detectable ctDNA, and both patients developed recurrent metastatic disease after completion of ribociclib with ET. Notably, one of these patients developed CNS-only disease. While follow-up is early, the remaining patients did not have detectable ctDNA and have not developed recurrent disease. This study suggests monitoring for ctDNA may identify patients at increased risk for recurrence in the extended adjuvant period and potentially guide therapy escalation.

Citation Format: Arielle J. Medford, Lauren Scarpetti, Andrzej Niemierko, Steven J. Isakoff, Beverly Moy, Seth A. Wander, Elizabeth Deluca, Elizabeth Abraham, Jennifer Shin, Lowell Schnipper, Amy E. Comander, Therese Mulvey, Erik Spickard, Ekaterina Kalashnikova, Angel Rodriguez, Leif Ellisen, Aditya Bardia, Laura M. Spring. Cell-free DNA monitoring in a phase II study of adjuvant endocrine therapy with CDK 4/6 inhibitor ribociclib for localized HR+/HER2- breast cancer (LEADER) [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 PD17-03.

Abstract OT3-15-01: TBCRC-053: P-RAD: A Randomized Study of Preoperative Chemotherapy, Pembrolizumab and No, Low or High Dose RADiation in Node-Positive, HER2-Negative Breast Cancer

Background: The introduction of immune checkpoint inhibitors (ICI) to standard neoadjuvant chemotherapy regimens has been shown to significantly improve outcomes in patients with triple negative breast cancer and is being investigated for high-risk hormone receptor-positive (HR+)/human epidermal growth factor-2 negative (HER2-) breast cancer. Preclinical evidence suggests radiation therapy (RT) can stimulate intra-tumoral T cell infiltration and enhance the expression and immune detection of tumor-specific neoantigens. This phase II pilot randomized study (NCT04443348) aims to evaluate the safety and efficacy of two different doses of preoperative primary tumor RT boost when combined with neoadjuvant pembrolizumab, then followed by standard neoadjuvant chemotherapy. Dual co-primary endpoints include determining the pathologic complete response (pCR) rate in the non-irradiated and pathologically confirmed metastatic axillary lymph node(s) in each treatment arm and quantifying tumor-infiltrating T lymphocytes in on-treatment (C1D14) tumor biopsies. We hypothesize that high-dose RT will increase the proportion of tumors with high T cell infiltration (i.e., top quartile) from 25% to 55%. Secondary endpoints include measuring residual cancer burden, evaluating tolerability of the regimen, and assessing quality of life. Exploratory endpoints include evaluation of treatment-associated changes in the tumor immune microenvironment, circulating immune cell analyses, and circulating tumor DNA kinetics. Methods: The study plans to enroll 128 participants with either triple negative (n=80) or high-risk HR=/HER2- (n=48) breast cancer who will be randomized to receive no, low (9 Gy), or high (24 Gy) dose of preoperative RT boost, after which 24 participants of either breast cancer subtype will be enrolled to an exploratory high dose proton therapy boost cohort. The eligibility criteria include patients who have biopsy-proven, axillary lymph node-positive breast cancer that is either triple negative (defined as ER&lt; 10%, PR&lt; 10%, and HER2-negative) or high-risk HR+/HER2- (grade III or having a high-risk genomic assay score). Study treatment is given in 6-week cycles, with 400 mg Pembrolizumab given on day 1 of each cycle. For those participants randomized to receive a preoperative RT boost, treatment is delivered in 3 fractions (3 × 3 Gy or 3 × 8 Gy) over consecutive business days, where one of the fractions is given on the same day as C1D1 Pembrolizumab. Standard neoadjuvant chemotherapy begins on C1D15 with paclitaxel (plus carboplatin for triple negative) administered weekly for 12 weeks, and then starting on C3D15, dose-dense doxorubicin/cyclophosphamide is administered every 2 weeks for 8 weeks. Following neoadjuvant treatment, participants will receive standard breast surgery (including removal of the pathologically confirmed metastatic lymph node) followed by adjuvant pembrolizumab, radiation therapy, and standard-of-care systemic therapy as clinically indicated. Tissue samples from the primary tumor and biopsy-proven lymph node are taken at baseline, C1D14, and at the time of surgery. There are eleven blood collection timepoints throughout the neoadjuvant and adjuvant settings. Participants will be followed for 2 years after surgery to assess safety and durability of responses. Results: This study has accrued 12 participants to date, including 10 with triple negative breast cancer and 2 with high-risk HR+/HER2- breast cancer. Formal results for this study are forthcoming, as the trial is actively accruing at 6 institutions, with plans to open at 3 more within the year. For persons with a specific interest in this trial, please contact Joseph Connolly, Multi-Center Coordinator, at jconnolly28@mgh.harvard.edu.

Citation Format: Joseph J. Connolly, Laura M. Spring, Alphonse G. Taghian, Michele Gadd, Laura Warren, Ana C. Garrido-Castro, Tari King, Elizabeth A. Mittendorf, Jose P. Leone, Dana L. Casey, Lisa Carey, Tiffany A. Traina, Yara Abdou, Atif Khan, George Plitas, Jean Wright, Cesar Augusto Santa-Maria, Lisa Jacobs, Rachel Blitzblau, E Shelley Hwang, Carey Anders, Ian Krop, Antonio C. Wolff, Alastair M. Thompson, Elyssa Denault, Gaorav Gupta, Alice Ho. TBCRC-053: P-RAD: A Randomized Study of Preoperative Chemotherapy, Pembrolizumab and No, Low or High Dose RADiation in Node-Positive, HER2-Negative 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 OT3-15-01.

Abstract GS2-03: GS2-03 TRIO-US B-12 TALENT: Neoadjuvant trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage breast cancer

Background: Although patients (pts) with hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently experience disease response to neoadjuvant therapy, fewer than 10% achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an unmet need. HER2 is expressed at a low level (IHC 1+ or 2+) in approximately 60-70% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved in the US for HER2-positive and HER2-low metastatic BC (with boxed warnings for interstitial lung disease). However, the efficacy of T-DXd in the neoadjuvant setting is not known. The primary objective of TALENT (TRIO-US B-12, NCT04553770) is to evaluate the clinical activity and safety of neoadjuvant T-DXd alone or in combination with endocrine therapy in pts with HR+/HER2-low early BC.

Methods: Men and women with previously untreated, operable invasive early stage, non-recurrent, HR+, HER2-low (IHC 1+ or 2+/ISH- by local or central review) BC measuring &gt; 2 cm were eligible. In stage 1 of clinical trial, participants were randomized 1:1 to receive T-DXd (5.4 mg/kg IV q21 days) alone, Arm A, or in combination with anastrozole AI (1 mg PO QD), Arm B. Originally 6 cycles (cy) were given but in 02/2022, an amendment increased the number of treatment cy from 6 to 8 for newly enrolled pts, or those who had not yet had surgery. Men and pre/peri-menopausal women randomized to Arm B also received a GnRH agonist. Stratification factors were HER2 expression (1+ vs. 2+) and menopausal status (men as postmenopausal). Tumor tissue collected at baseline, cy 1 day 17-21, and at surgery. Breast imaging performed at baseline, cy 2 and pre-surgery/EOT. Primary endpoint is pCR rate (ypT0/is ypN0) at surgery. In stage 1, intent was to randomize 58 pts (if at least 2 pCR occurred in an arm, arm progresses to Stage 2 and an additional 15 pts to be enrolled). Other endpoints include safety, objective response rate (ORR), changes in Ki67 expression, Residual Cancer Burden index, exploratory biomarker analysis, and health-related quality of life. Here we present results from stage 1 of the trial.

Results: From 09/21/2020 to 10/13/2022, 58 pts were enrolled and treated (29 Arm A, 29 Arm B) in stage 1 of trial. Five pts came off study before completing study therapy (2 after cy 1, 2 after cy 2, 1 after cy 3). As of data cut-off (10/05/2022), 33 pts completed study treatment and have had surgery (17 Arm A, 16 Arm B), 13 are on treatment and 7 are pending surgery; 27 pts completed 6 cy and 13 completed 8 cy. Baseline characteristics were balanced between arms. 19/58 pts were Stage IIA, 26/58 Stage IIB, 12/58 Stage IIIA, and 1/58 Stage IIIB at baseline. 46/58 pts had baseline HER2 expression (from central review) of 1+, 4/58 were 0, 6/58 were 2+, 1/58 had multicentric lesion 1+ and 2+, and 1/58 had a single lesion with 1+ and 2+. In Arm A, 1/17 pt had pCR after 8 cy, 2/17 pts had RCB-I after 6 cy (17.6% RCB 0/1). In Arm B, 1/16 pt had RCB-I after 8 cy (6.3%). The ORR for response-evaluable pts in Arm A was 75% (12/16, 1 CR, 11 PR) and in Arm B was 63.2% (12/19, 2 CR, 10 PR); 1 patient (Arm B) had PD. ILD occurred in 1 pt (1.7%), Gr 2 and resolved 11 days after stopping therapy. Most common treatment-related Grade ≥ 3 AEs in Arms A and B, respectively, include hypokalemia (1.7%, 5.2%), diarrhea (3.4%, 3.4%), neutropenia (3.4%, 1.7%), fatigue (1.7%, 3.4%), headache (3.4%, 1.7%), vomiting (3.4%, 1.7%), dehydration (1.7%, 1.7%) and nausea (3.4%, 0%).

Conclusions: This is the first report of a trial evaluating neoadjuvant T-DXd in HER2 low breast cancer. T-DXd +/- endocrine therapy demonstrates promising clinical activity for pts with HR+ BC. Updated study results will be provided at the time of presentation.

Citation Format: Aditya Bardia, Sara Hurvitz, Michael F. Press, Lisa S. Wang, Nicholas P. McAndrew, David Chan, Vu Phan, Deborah Villa, Merry L. Tetef, Erin Chamberlain, Nihal Abdulla, Thomas Lomis, Laura M. Spring, Steven Applebaum, Shaker Dakhil, Brian DiCarlo, David D. Kim, Evangelia Kirimis, William E. Lawler, Aashini K. Master, Kelly McCann, Edwin Hayashi, Christine Kivork, James Chauv. GS2-03 TRIO-US B-12 TALENT: Neoadjuvant trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage 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 GS2-03.

Abstract P1-08-01: Virtual molecular and precision medicine (vMAP) clinic to improve access to clinical trials for patients with metastatic breast cancer: an academic-community collaboration

Background: Despite improved outcomes for patients with metastatic breast cancer (MBC), attributed in part to advancements in precision therapeutics, clinical trial enrollment and genomic testing are relatively underutilized in the community oncology setting. To address this need, we launched a virtual molecular and precision medicine (vMAP) clinic to improve access for patients in our community network. Here we describe the initial results from the virtual clinic initiative. Methods: In 2020, the vMAP clinic was launched to provide real-time access to precision medicine expertise through virtual, email-based consultation directed to a multidisciplinary team. As part of the service, providers contacted vMAP regarding patients with MBC at the time of initial presentation or disease progression. Upon receipt, the vMAP team (including breast medical oncologists, a breast oncology research nurse, a research assistant, and ad hoc consultation from cancer genetics and molecular pathology representatives) engaged in discussion to identify potential clinical trials with slot availability or standard of care (SOC) options and provided recommendations to the referring provider within 72 hours. Relevant patient data and vMAP referral outcomes were recorded. Providers across the community network were surveyed at project onset and after seventeen months. Results: In its first 14-month period (June 2020-July 2021), 47 cases from 16 providers across seven community oncology sites and one academic site were referred to vMAP. A majority (88.6%) of patients had undergone somatic genomic testing (tissue-based, plasma-based, or both) to inform treatment guidance. All cases were screened for available clinical trials as well as SOC options at the time of referral. The average response time to the referring provider with a finalized recommendation was 1.77 days (range 0-5). Forty cases (85.1%) had clinical trial options identified on vMAP pre-screen. Subsequently, 22 patients (46.8%) screened for vMAP recommended clinical trials with 18 (38.3%) initiating enrollment. Of the remaining patients that did not pursue clinical trial screening, 17 (36.2%) started vMAP-recommended SOC treatment, five (10.6%) pursued a different treatment, one (2.1%) was not a candidate for further treatment, and two (4.3%) opted to receive care at a non-affiliated institution, and subsequent treatment information was not available. Reasons that patients did not enroll on trials included trial ineligibility, formal clinical trial screening failure, and patient/provider preference. At project onset, network provider survey results confirmed a previously suggested demand for improvements in processes surrounding genomic testing interpretation and clinical trial enrollment. Post-referral survey results indicated vMAP recommendations and pre-screenings improved the processes surrounding interpretation of genomic testing and clinical trial screening and enrollment, with high rates of referring provider satisfaction. Conclusion: A precision medicine virtual clinic demonstrated an efficient and flexible means to offer real-time interpretation of genomic and molecular test results and identification of appropriate treatment options, including clinical trials when applicable, for patients with MBC. The service highlights an example of an academic-community collaboration model to expand precision medicine and clinical trial access for patients with metastatic breast cancer.

Citation Format: Lindsey Mortensen, Jennifer C. Keenan, Elizabeth Abraham, Sarah Padden, Annie Ma, Elyssa Denault, Lianne Ryan, Arielle J. Medford, Leif Ellisen, Joel H. Schwartz, Aditya Bardia, Laura M. Spring. Virtual molecular and precision medicine (vMAP) clinic to improve access to clinical trials for patients with metastatic breast cancer: an academic-community collaboration [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 P1-08-01.

Abstract P1-13-07: Investigating NF1 Mutations in Circulating Tumor DNA of Patients with Hormone-receptor Positive (HR+) Breast Tumors Resistant to CDK4/6 Inhibition (CDK4/6i): A Retrospective Clinical Analysis

Background: CDK4/6 inhibitors (CDK4/6i) are standard of care for the management of HR+/HER2- metastatic breast cancer (MBC). Genomic alterations that drive resistance to CDK4/6i are diverse, and while the molecular landscape is heterogeneous, several mechanisms of CDK4/6i resistance converge on the RAS/MAPK and PI3K/AKT/mTOR signaling pathways. NF1 downregulates RAS and dampens cellular proliferation. Laboratory-based models demonstrate that loss of NF1 is associated with resistance to endocrine therapy (ET), and emergence of NF1 mutations (NF1m) are correlated with progressive disease (PD) in circulating tumor DNA (ctDNA). While NF1m may diminish CDK4/6i susceptibility, a clear relationship has not been elucidated. The primary objective of this study was to characterize patient (pt) response to CDK4/6i in NF1m HR+/HER2- MBC. Methods: We identified 47 pts with NF1m via a database with one or more ctDNA samples sequenced at variable time-points as part of routine care for MBC. NF1m were categorized as pathogenic (p)NF1m or variants of uncertain significance (VUS) based on their associated Guardant report. We identified 27 pts with HR+/HER2- MBC and NF1m that received at least 1 line of CDK4/6i in the metastatic setting. Intrinsic resistance was defined as PD &lt; 6 months on a CDK4/6i regimen, and acquired resistance was defined as PD &gt;6 months. Pts with intrinsic resistance or acquired resistance and NF1m detected post-PD were categorized as having a resistance phenotype potentially driven by NF1m. Pts with NF1m detected prior to therapy and &gt;6 months clinical response on a CDK4/6i were categorized as having NF1m tumors sensitive to CDK4/6i. Results: The NF1m cohort (n = 27) had 9 pts with pNF1m, while 18 pts expressed VUS. The median age at MBC diagnosis was 54 years, and 67% had visceral metastasis at ctDNA collection. Pts received a median of 1 prior line (range: 0 - 6) of ET or chemotherapy in the metastatic setting before CDK4/6i. Amongst pts with pathogenic variants (n = 9), we found 3 pts with pNF1m were intrinsically resistant to CDK4/6i. Acquired resistance was seen in 1 pt with pNF1m detected post-PD, and 2 pts had evidence of both acquired and subsequent intrinsic resistance to a later line of CDK4/6i. Overall, 67% (6/9) of pNF1m pts demonstrated a CDK4/6i resistance phenotype; mutant allele fraction (AF) ranged from 0.2% - 29.9%, and the mean maximum allele fraction (MAF) was 6.0%. Pre- and post-treatment samples were available on 3 pts with pNF1m, and 1 of these pts had an AF rise from 2.7% to 12.3% when comparing ctDNA pre- and post-CDK4/6i. ctDNA from 4 of 6 resistant tumors harbored other putative drivers including alterations in FGFR, KRAS, PTEN, and RB. We identified 2 counter-examples of pNF1m tumors sensitive to CDK4/6i. These pts expressed relatively low NF1m AF, ranging 0.1% - 0.5% with a mean MAF 0.3%. Another pNF1m pt had intrinsic resistance to initial CDK4/6i but was sensitive to later-line CDK4/6i. In the subgroup of pts with VUS-NF1m (n = 18), a more mixed picture of resistance and sensitivity was seen. 8 pts had intrinsic or acquired resistance, 8 pts had NF1m tumors sensitive to CDK4/6i, and 1 pt had evidence of both; 61% (n = 11) of pts expressed alterations in other resistance mediating genes. 1 pt stopped therapy due to toxicity rather than PD. Conclusions: Our work demonstrates that tumor expression of pNF1m may be associated with CDK4/6i resistance in pts with HR+/HER2- MBC, and allele fraction could be predictive of drug susceptibility. Tumors harboring VUS had varied sensitivity, suggesting that some of these mutations may not be pathogenic, and counter-examples of pNF1m MBC benefiting from CDK4/6i plus ET highlight the complexities in predicting drug response based on single gene alteration. Future effort is warranted to explore the potential impact of NF1 on CDK4/6i resistance, as well as the potential role for therapies targeting the MAPK pathway in this patient population.

Citation Format: Maxwell R. Lloyd, Lianne Ryan, Arielle J. Medford, Jennifer C. Keenan, Laura M. Spring, Neelima Vidula, Beverly Moy, Dejan Juric, Leif Ellisen, Aditya Bardia, Seth A. Wander. Investigating NF1 Mutations in Circulating Tumor DNA of Patients with Hormone-receptor Positive (HR+) Breast Tumors Resistant to CDK4/6 Inhibition (CDK4/6i): A Retrospective Clinical Analysis [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 P1-13-07.

Abstract HER2-19: HER2-19 Impact of HER2 low status on clinical outcomes in participants with 1-3 positive lymph nodes, HR+/HER2- breast cancer with recurrence score &lt;/25 randomized to endocrine therapy +/- chemotherapy: results from SWOG S1007 (RxPONDER)

Background: HER2 low breast cancer, defined as tumors with HER2 IHC expression 1+ or 2+ without HER2 gene amplification, represents a potential new therapeutic subgroup of metastatic breast cancer (BC). However, the clinical significance of HER2 low status in early BC remains unclear. Previously, the RxPONDER trial (NCT01272037), a prospective, randomized trial of endocrine therapy (ET) vs. chemoendocrine therapy (CET) in women with lymph node positive (LN+) BC, demonstrated invasive disease-free survival (IDFS) with ET vs CET varies by menopausal status. We evaluated the impact of HER2 low vs zero status in the RxPONDER trial (SWOG S1007), stratified by menopausal status and treatment groups.

Methods: Eligibility criteria included women &gt;/18 years of age with hormone receptor-positive (HR+), HER2-negative (HER2-) BC, Recurrence Score (RS) &lt;/25, 1-3+ LN and no contraindications to taxane and/or anthracycline based CT. The impact of HER2 low status and other baseline clinicopathological features on clinical outcomes were evaluated using covariates in Cox regression analysis. HER2 IHC status was per local testing. HER2 low was defined as IHC 1+ or IHC 2+ without HER2 gene amplification, and HER2 zero was defined as IHC 0. The primary endpoint was IDFS, defined as the time from the date of randomization to the date of a first invasive recurrence (local, regional, or distant), a new invasive primary cancer (breast cancer or another type of cancer), or death from any cause. Secondary objectives included distant-relapse free survival (DRFS).

Results: Among the 4,983 eligible participants, 4,588 had IHC HER2 status available. 52% of 2,052 pre-menopausal women had HER2 low BC and 57% of 3,042 post-menopausal women had HER2 low BC. There was a small, but statistically significant (p=0.03) difference, in RS between HER2 low (mean 14.5) and HER2 zero (mean 14.1) status. The proportion of participants with HER2 low and zero were balanced between treatment group assignment (CET vs ET). Among pre-menopausal women adjusting for RS, CET led to an observed improvement in IDFS among both HER2 low (HR=0.67; 95% CI 0.43-1.04) and HER2 zero subgroups (HR=0.57; 95% CI 0.36-0.89) (interaction p=0.55). Similarly, among post-menopausal women, there was no difference in IDFS between CET vs ET among both HER2 low (HR=0.98; 95% CI 0.75-1.29) and HER2 zero (HR=1.12; 95% CI 0.80-1.56) subgroups (interaction p=0.57). In multivariable analysis, adjusting for treatment arm, RS, and menopausal status, HER2 low status was not associated with worse IDFS compared to HER2 zero status (HR=0.93; 95% CI 0.78-1.11). Additionally, no differences were noted in DRFS.

Conclusion: HER2 low or zero status had no impact on clinical outcomes with CET vs ET among pre-menopausal or post-menopausal women with HR+/HER- BC with 1-3+ LNs and RS &lt;/25. HER2 low evaluation should not be currently used for CET vs ET clinical decision making among patients with HR+/HER2- breast cancer with 1-3+ LN and RS &lt;/25. Further research on the role of HER2 low status in other settings may be warranted.

Citation Format: Laura M. Spring, William E. Barlow, Aditya Bardia, Priyanka Sharma, Lajos Pusztai, Gabriel N. Hortobagyi, Kevin Kalinsky. HER2-19 Impact of HER2 low status on clinical outcomes in participants with 1-3 positive lymph nodes, HR+/HER2- breast cancer with recurrence score &lt;/25 randomized to endocrine therapy +/- chemotherapy: results from SWOG S1007 (RxPONDER) [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 HER2-19.

Abstract P5-02-07: Cell-free DNA detection of GATA3 mutations in metastatic hormone receptor positive breast cancer: a retrospective, observational multi-institutional analysis

Background GATA3 mutations (GATA3mut) have been reported in 10-20% of hormone receptor positive (HR+) breast cancers. It has been shown that targeting GATA3mut HR+ breast cancer with MDM2 inhibitors invokes synthetic lethality. MDM2 is an E3 ubiquitin ligase that targets p53 for degradation, and research suggests that restoring p53 by blocking MDM2 may be effective in treating GATA3mut HR+ breast cancer. One potential mechanism of this efficacy has been shown to be through the PI3K-AKT pathway. We thus sought to characterize the GATA3mut landscape in a multi-institutional cell-free DNA (cfDNA) analysis and to determine the association between GATA3mut and TP53 mutations, as well as alterations in the PI3K-AKT pathway and the impact of GATA3 on survival. Methods We analyzed cfDNA data collected at the Massachusetts General Hospital and at Washington University in St Louis via Guardant360, a next generation sequencing assay that analyzed up to 74 genes during the study period. The association of GATA3mut and co-mutations as well as number of prior therapies was estimated using Pearson’s chi-squared test for categorical variables, two-sample Wilcoxon rank-sum test for continues variables, and multivariable logistic regression. The impact of GATA3mut and GATA3 wildtype (WT) on progression-free survival (PFS) and overall survival (OS) was analyzed using multivariable Cox regression analysis, adjusting for age, number of prior therapies, visceral metastases, and de novo metastases. PFS and OS were evaluated in the overall study population, as well as in subgroups of patients that received endocrine monotherapy and chemotherapy. Results Out of 647 patients with HR+ MBC, 10% (n = 68) had non-synonymous GATA3 mutations. Among these 68 GATA3mut patients, 37% (n = 25) were mutations in exon 5, all but two of which were in the second zinc finger, and 62% (n = 42) were in exon 6. 62% (n = 42) were frameshift mutations, 20% (n = 14) were indels, and 18% (n = 12) were point mutations. Median mutant allele fraction (MAF) of GATAmut was 0.95% (range 0.03 – 30.5%). There was no statistically significant association of GATA3mut with the number of prior therapies, PR status, or the presence of ESR1, TP53, or PI3K-AKT pathway mutations. In the GATA3mut population, TP53 co-mutations (n = 21) were found with a median MAF of 0.6%. PI3K-AKT pathway alterations occurred in 47% (n=32) of GATA3mut patients (PIK3CA n = 27; AKT n = 2; PTEN n = 3). In the combined cohort, there was no significant difference in PFS or OS after adjusting for visceral metastases, de novo disease, number of prior therapies, and age. In a cohort of 80 patients that received endocrine monotherapy (GATA3 WT n = 74, GATA3mut n = 6), GATA3mut were associated with borderline worse PFS (HR 2.6; p = 0.061) and worse OS (HR 4.5; p = 0.009). There was no statistically significant difference in PFS or OS in a subgroup that received chemotherapy. Conclusions GATA3 mutations can be identified via cfDNA in patients with HR+ MBC. Co-mutations in TP53 occurred at overall low MAF. Further research is needed to characterize the functional impact of these low level TP53 co-mutations and develop therapeutic strategies to target GATA3 mutant MBC.

Citation Format: Arielle J. Medford, Marko Velimirovic, Andrzej Niemierko, Whitney L. Hensing, Andrew A. Davis, Katherine K. Clifton, Jennifer C. Keenan, Charles S. Dai, Lesli A. Kiedrowski, Ami N. Shah, Lorenzo Gerratana, Laura M. Spring, Leif Ellisen, Robert C. Doebele, Massimo Cristofanilli, Aditya Bardia. Cell-free DNA detection of GATA3 mutations in metastatic hormone receptor positive breast cancer: a retrospective, observational multi-institutional analysis [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 P5-02-07.

Mechanisms of Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs), with antibodies targeted against specific antigens linked to cytotoxic payloads, offer the opportunity for a more specific delivery of chemotherapy and other bioactive payloads to minimize side effects. First approved in the setting of HER2+ breast cancer, more recent ADCs have been developed for triple-negative breast cancer (TNBC) and, most recently, hormone receptor-positive (HR+) breast cancer. While antibody-drug conjugates have compared favorably against traditional chemotherapy in some settings, patients eventually progress on these therapies and require a change in treatment. Mechanisms to explain the resistance to ADCs are highly sought after, in hopes of developing next-line treatment options and expanding the therapeutic windows of existing therapies. These resistance mechanisms are categorized as follows: change in antigen expression, change in ADC processing and resistance, and efflux of the ADC payload. This paper reviews the recently published literature on these mechanisms as well as potential options to overcome these barriers.

Current and Emerging Role of Antibody-Drug Conjugates in HER2-Negative Breast Cancer

Antibody-drug conjugates (ADCs) are rapidly evolving therapies that are uniquely able to deliver potent chemotherapy specifically to cancer cells while largely sparing normal cells. ADCs have 3 components: (1) antibody targeted to a tumor-involved antigen, (2) cytotoxic payload, and (3) linker that connects the cytotoxic agent to the antibody. Once the antibody binds the target on the cell surface, the ADC is incorporated into the cell via receptor-mediated endocytosis. Inside the cells, the linker is cleaved in the lysosome and the payload is then released intracellularly. This article will review ADCs in clinical development for HER2-negative metastatic breast cancer.

TRK inhibitor in a patient with metastatic triple-negative breast cancer and NTRK fusions identified via cell-free DNA analysis

Tissue-agnostic indications for targeted therapies have expanded options for patients with advanced solid tumors. The Food and Drug Administration approvals of the programmed death-ligand 1 inhibitor pembrolizumab and the TRK inhibitors larotrectinib and entrectinib provide rationale for next-generation sequencing (NGS) in effectively all advanced solid tumor patients given potential for clinical responses even in otherwise refractory disease. As proof of concept, this case report describes a 64-year-old woman with triple-negative breast cancer refractory to multiple lines of therapy, found to have a rare mutation on NGS which led to targeted therapy with meaningful response. She initially presented with metastatic recurrence 5 years after treatment for a localized breast cancer, with rapid progression through four lines of therapy in the metastatic setting, including immunotherapy, antibody-drug conjugate-based therapy, and chemotherapy. Germline genetic testing was normal. Ultimately, NGS evaluation of cell-free DNA via an 83-gene assay (Guardant Health, Inc.) identified two NTRK3 fusions: an ETV6-NTRK3 fusion associated with the rare secretory breast carcinoma, and CRTC3-NTRK3, a novel fusion partner not previously described in breast cancer. Liver biopsy was sent for whole exome sequencing and RNA-seq analysis of tissue (BostonGene, Inc., Boston, MA, USA), which provided orthogonal confirmation of both the ETV6-NTRK3 and CRTC3-NTRK3 fusions. She was started on the TRK inhibitor larotrectinib with a marked clinical and radiographic response after only 2 months of therapy. The patient granted verbal consent to share her clinical story, images, and data in this case report. This case demonstrates the significant potential benefits of NGS testing in advanced cancer and the lessons we may learn from individual patient experiences.

Adjuvant trastuzumab and vinorelbine for early-stage HER2+ breast cancer

Background

The single-arm phase II APT trial established trastuzumab and paclitaxel (TH) as the standard adjuvant regimen for small human epidermal growth factor receptor 2 (HER2+) tumors. However, paclitaxel causes alopecia and has high rates of neuropathy and hypersensitivity reactions. In patients with metastatic HER2+ breast cancer (BC), the combination of trastuzumab and vinorelbine (TV) is effective and well tolerated. There is a need for alternative non-anthracycline/taxane-based regimens for patients with HER2+ early-stage BC, especially for those with contraindications or who wish to avoid side effects of taxane-based regimens. Here we describe our institutional experience with adjuvant TV for patients with early-stage HER2+ BC.

Methods

Clinicopathological characteristics, treatment details, and outcomes of patients with localized HER2+ BC treated with adjuvant TV from 2007 to 2021 at a large academic medical institution were collected. Study endpoints included invasive disease-free survival (IDFS), overall survival (OS), and safety/tolerability. IDFS and OS were measured from start date of TV treatment to date of event/last follow-up and date of death/last follow-up, respectively.

Results

A total of 30 patients were treated with TV. All patients received trastuzumab at standard dosing and vinorelbine at a starting dose of 25 mg/m² either on days 1/8 or on days 1/8/21 (weekly) of a 21-day cycle with four planned cycles. Median age at diagnosis was 59 years (range: 36-81). 90.3% of patients had anatomic pathologic stage IA BC and 9.7% stage IIA BC. Of the 30 patients, 24 of them opted to pursue TV due to concerns related to alopecia, neuropathy, and other toxicities, and 6 switched from treatment with TH to TV due to toxicities. Eight patients experienced neutropenia with no cases of febrile neutropenia. No patients experienced alopecia or long-term neuropathy. With a median follow-up of 68 months (5.7 years), the 5-year IDFS rate was 90.9%, with one local and one distant recurrence. The 5-year OS was 100%.

Conclusions

Trastuzumab in combination with vinorelbine in the adjuvant, early-stage setting for low-risk HER2+ BC demonstrated clinical efficacy and appeared to be well tolerated. TV warrants further evaluation as an alternative regimen to TH for patients with early-stage HER2+ BC.

Clinical Implications and Treatment Strategies for ESR1 Fusions in Hormone Receptor-Positive Metastatic Breast Cancer: A Case Series

In hormone receptor-positive metastatic breast cancer (HR+ MBC), endocrine resistance is commonly due to genetic alterations of ESR1, the gene encoding estrogen receptor alpha (ERα). While ESR1 point mutations (ESR1-MUT) cause acquired resistance to aromatase inhibition (AI) through constitutive activation, far less is known about the molecular functions and clinical consequences of ESR1 fusions (ESR1-FUS). This case series discusses 4 patients with HR+ MBC with ESR1-FUS in the context of the existing ESR1-FUS literature. We consider therapeutic strategies and raise the hypothesis that CDK4/6 inhibition (CDK4/6i) may be effective against ESR1-FUS with functional ligand-binding domain swaps. These cases highlight the importance of screening for ESR1-FUS in patients with HR+ MBC while continuing investigation of precision treatments for these genomic rearrangements.

Implementation and Clinical Adoption of Precision Oncology Workflows Across a Healthcare Network

BACKGROUND

Precision oncology relies on molecular diagnostics, and the value-proposition of modern healthcare networks promises a higher standard of care across partner sites. We present the results of a clinical pilot to standardize precision oncology workflows.

METHODS

Workflows are defined as the development, roll-out, and updating of disease-specific molecular order sets. We tracked the timeline, composition, and effort of consensus meetings to define the combination of molecular tests. To assess clinical impact, we examined order set adoption over a two-year period (before and after roll-out) across all gastrointestinal and hepatopancreatobiliary (GI) malignancies, and by provider location within the network.

RESULTS

Development of 12 disease center-specific order sets took ~9 months, and the average number of tests per indication changed from 2.9 to 2.8 (P = .74). After roll-out, we identified significant increases in requests for GI patients (17%; P < .001), compliance with testing recommendations (9%; P < .001), and the fraction of "abnormal" results (6%; P < .001). Of 1088 GI patients, only 3 received targeted agents based on findings derived from non-recommended orders (1 before and 2 after roll-out); indicating that our practice did not negatively affect patient treatments. Preliminary analysis showed 99% compliance by providers in network sites, confirming the adoption of the order sets across the network.

CONCLUSION

Our study details the effort of establishing precision oncology workflows, the adoption pattern, and the absence of harm from the reduction of non-recommended orders. Establishing a modifiable communication tool for molecular testing is an essential component to optimize patient care via precision oncology.

Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer

Purpose

To explore the immunogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with breast cancer based on type of anticancer treatment.

Methods

Patients with breast cancer had anti-spike antibody concentrations measured ⩾14 days after receiving a full SARS-CoV-2 vaccination series. The primary endpoint was IgA/G/M anti-spike antibody concentration. Multiple regression analysis was used to analyze log₁₀-transformed antibody titer concentrations.

Results

Between 29 April and 20 July 2021, 233 patients with breast cancer were enrolled, of whom 212 were eligible for the current analysis. Patients who received mRNA-1273 (Moderna) had the highest antibody concentrations [geometric mean concentration (GMC) in log₁₀: 3.0 U/mL], compared to patients who received BNT162b2 (Pfizer) (GMC: 2.6 U/mL) (multiple regression adjusted p = 0.013) and Ad26.COV2.S (Johnson & Johnson/Janssen) (GMC: 2.6 U/mL) (p = 0.071). Patients receiving cytotoxic therapy had a significantly lower antibody titer GMC (2.5 U/mL) compared to patients on no therapy or endocrine therapy alone (3.0 U/mL) (p = 0.005). Patients on targeted therapies (GMC: 2.7 U/mL) also had a numerically lower GMC compared to patients not receiving therapy/on endocrine therapy alone, although this result was not significant (p = 0.364). Among patients who received an additional dose of vaccine (n = 31), 28 demonstrated an increased antibody response that ranged from 0.2 to >4.4 U/ mL.

Conclusion

Most patients with breast cancer generate detectable anti-spike antibodies following SARS-CoV-2 vaccination, though systemic treatments and vaccine type impact level of response. Further studies are needed to better understand the clinical implications of different antibody levels, the effectiveness of additional SARS-CoV-2 vaccine doses, and the risk of breakthrough infections among patients with breast cancer.

Abstract 5248: CDK4/6 inhibition (CDK4/6i) is effective in the real-world setting for hormone receptor-positive metastatic breast cancer (HR+ MBC) with ESR1 mutations and fusions

Background For HR+ MBC, ESR1 point mutations (ESR1-MUT) are a common mechanism of acquired resistance to aromatase inhibition (AI); ESR1 fusions (ESR1-FUS) are rare and promote intrinsic resistance to ER-targeting drugs. Retrospective analyses of CDK4/6i trials suggest ESR1-MUT does not cause CDK4/6i resistance, but whether CDK4/6i is effective for ESR1-MUT, or for ESR1-FUS, in the real-world setting is unknown.

Methods Real-world evidence was sourced from the GuardantInform database of commercial payer claims and ctDNA tests from 170,000+ individuals. Patients with MBC who started CDK4/6i within 30 days of ctDNA testing were categorized as ESR1-MUT vs. ESR1-WT and analyzed for time-to-next-treatment (TTNT). Separately, cases with ESR1-FUS detected by tissue RNA-Seq were extracted from a clinicopathologic database at an academic cancer center.

Results There was no significant difference in TTNT on CDK4/6i for ESR1-MUT vs. ESR1-WT. As expected, ESR1-MUT had shorter overall survival (OS), even after adjustment for age, CDK4/6i drug, and prior treatment (HR 0.58 (0.42-0.82), p=0.002, multivariable Cox). Endocrine partner analysis was limited by lack of clinical annotation to 27% of cases: AI was given to 55% of ESR1-WT and 25% of ESR1-MUT; fulvestrant was given to 39% of ESR1-WT and 68% of ESR1-MUT. Additional stratified analyses will be presented.

In the clinicopathologic database, we identified 4 ESR1-FUS cases, and all received CDK4/6i. Progression-free survival durations on CDK4/6i were 4, 10, 11, and 33+ months.

Conclusions Using real-world evidence, we demonstrate that CDK4/6i is effective in both ESR1-MUT and ESR1-WT HR+ MBC, supporting the use of CDK4/6i in this setting. CDK4/6i may be additionally beneficial for patients with ESR1-FUS. Future directions include expanding the ESR1-FUS cohort and deciphering the heterogeneity of CDK4/6i responses in this patient population.

ESR1-WT ESR1-MUT p-value n=612 n=145 TTNT, median days (95% CI) 99 (85-121) 102 (85-152) 0.84 (log-rank) OS, median years (95% CI) 5.1 (4.5-NA) 2.2 (2.0-NA) &lt;0.0001 (log-rank) CDK4/6i drug palbociclib: 71.1% ribociclib: 9.8% abemaciclib: 19.1% palbociclib: 60% ribociclib: 5.5% abemaciclib: 34.5% 0.038 (chi-square) Prior lines of treatment 0: 21.2% 1: 26.1% 2: 18.6% 3+: 34.0% median: 2 0: 15.9% 1: 22.8% 2: 17.2% 3+: 44.1% median: 2 0.013 (Mann-Whitney U)

Citation Format: Jamie O. Brett, Caroline M. Weipert, Lauren L. Ritterhouse, Nicole Zhang, Junhua Yu, Lianne Y. Ryan, Laura M. Spring, Miguel N. Rivera, Jochen K. Lennerz, Dora Dias-Santagata, Leif W. Ellisen, Aditya Bardia, Seth A. Wander. CDK4/6 inhibition (CDK4/6i) is effective in the real-world setting for hormone receptor-positive metastatic breast cancer (HR+ MBC) with ESR1 mutations and fusions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5248.

The Evolving Role of Neoadjuvant Therapy for Operable Breast Cancer

The role of neoadjuvant therapy (NAT) for localized breast cancer has evolved tremendously over the past several years. Currently, NAT is the preferred option for high-risk early triple-negative (TN) and HER2-positive (HER2+) breast cancers and is indicated for some estrogen receptor-positive (ER+) breast cancers. In addition to traditional absolute indications for NAT, relative indications such as the assessment of outcomes at the time of surgery and guidance of treatment escalation and de-escalation have greatly evolved in recent years. Pathologic complete response (pCR) and the Residual Cancer Burden (RCB) index are highly prognostic for disease recurrence and survival, mainly in patients with TN or HER2+ disease. Furthermore, post-NAT escalation strategies have been shown to improve long-term outcomes of patients who do not achieve pCR. Additionally, by allowing the direct assessment of drug effect on the tumor, the neoadjuvant setting has become an attractive setting for the exploration of novel agents and the identification of predictive biomarkers. Neoadjuvant trial design has also evolved, using adaptive treatment approaches that enable treatment de-escalation or escalation based on response. However, despite multiple practice-changing neoadjuvant trials and the addition of various new agents to the neoadjuvant setting for early breast cancer, many key questions remain. For example, patient selection for neoadjuvant immunotherapy in TN breast cancer, de-escalation methods in HER2+ breast cancer, and the use of gene expression profiles to guide NAT recommendations in ER+ breast cancer. This article reviews the current approach for NAT in localized breast cancer as well as evolving NAT strategies, the key remaining challenges, and the ongoing work in the field.

Abstract OT1-12-05: Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage breast cancer

Background Although patients with clinical response of hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently respond to neoadjuvant therapy, fewer than 10% of patients achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with targeted agents such as CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an area of unmet need. HER2 amplification is a known driver of endocrine resistance and HER2 may be expressed at a low level (IHC 1+ or 2+) in up to 60% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved for HER2-positive metastatic BC and has demonstrated promising clinical efficacy in HER2-low BC with an objective response rate of ~37%. The aim of TALENT (TRIO-US B-12) is to evaluate the clinical activity and toxicity of neoadjuvant T-DXd either alone or in combination with endocrine therapy in patients with HR+/HER2-low early BC. Methods TRIO-US B-12 TALENT (NCT04553770) is an ongoing randomized, multicenter, open-label, two-stage, phase II neoadjuvant trial for participants with early stage, HR+, HER2-low expressing (1+ or 2+ by IHC) BC. Eligible participants include men and women with previously untreated, operable invasive BC greater than 2.0 cm (cT2) in size. Pts with recurrent or metastatic BC, or inflammatory BC are excluded. Pts are randomized 1:1 to receive six cycles of T-DXd (5.4 mg/kg IV q21 days) either alone or in combination with anastrozole AI (1 mg PO QD). Men and pre/peri menopausal women randomized to the AI arm also receive standard of care GnRH agonist. Stratification factors include HER2 expression (1+ or 2+) and menopausal status (men stratified as post-menopausal). Tumor tissue is taken at baseline, cycle 1 day 17-21, and at surgery. Blood samples are taken at four time points for biomarker analysis. The primary endpoint is pCR rate (breast and lymph node) at definitive surgery. In stage I, 58 participants will be randomized (29/arm). If ≥2 participants in an arm achieve pCR, that arm will expand (stage II) to enroll an additional 15 participants (total of 44/arm). A pCR rate of &gt;10% (5/44) would be considered favorable, warranting further evaluation of the treatment in a larger trial. Other endpoints include safety, changes in Ki67 expression, Residual Cancer Burden index, biomarker analysis (including serial cfDNA analysis), and health-related quality of life. As of June 2021, sixteen participants have enrolled. Conclusions To our knowledge this is the first and only ongoing study evaluating T-DXd with or without endocrine therapy for HR+, HER2-low breast cancer in the neoadjuvant setting. The study will shed light on clinical activity and biomarkers, which may guide larger confirmatory studies for patients with HR+, HER2-low early breast cancer.

Citation Format: Sara Hurvitz, Aditya Bardia, Merry L. Tetef, Nicholas P. McAndrew, Steven Applebaum, Aashini K. Master, Maggie L. DiNome, Minna K. Lee, Evangelia Kirimis, David D. Kim, Lisa S. Wang, Kyle Greene, Vu Phan, Nihal Abdulla, David Chan, Laura M. Spring, Christine Kivork, James Chauv. Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-12-05.

Abstract P1-18-22: AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation

Background: The cyclin-dependent kinase 4/6 inhibitors, with endocrine therapy (ET), have become the standard of care for patients with HR+/HER2- MBC. Prior insight from tumor biopsies and preclinical analyses suggest that AKT1 activation can provoke CDK4/6i resistance, highlighting a potential therapeutic role for AKT inhibition (AKTi) in this setting. However, combinatorial inhibition can be associated with significant toxicity and identification of the optimal biological dose is often challenging. In this translational co-clinical study, we evaluated escalating doses of AKTi combination with CDK 4/6i in parallel patient-derived pre-clinical models as well as a phase 1b clinical trial. Methods: In an open-label phase Ib dose-escalation clinical trial (TAKTIC, NCT03959891), we evaluated the safety, tolerability and efficacy of escalating doses of the AKT1 inhibitor ipatasertib (ipat) in combination with palbociclib (palbo) and fulvestrant (fulv) for patients with HR+/HER2- MBC. Inclusion criteria include unresectable or metastatic disease, at least 1 prior therapy for MBC including any CDK4/6i, and up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). In addition, response to escalating doses of ipat and palbo (with fulv) were explored in vitro via an ATP-based viability assay in tumor cell lines derived from circulating tumor cells (CTC) isolated from patients with endocrine-refractory HR+ MBC. Results: In the dose-escalation portion of the phase 1b clinical trial, 23 patients received the triplet combination of ipat, palbo, and fulv (median number of prior lines = 4.3, range 1-7; 100% with prior CDK4/6i): 3 pts received ipat at 200mg + 125mg palbo, 15 pts received 300mg + 125mg palbo, and 5 pts received 400mg + 100mg palbo, all with fulv (500 mg). Among the 23 patients, 20 patients (86.9%) had disease control (4 partial response and 16 stable disease) as the best response, per RECIST. Grade 3/4 toxicities included neutropenia (n=20), lymphopenia (n=3), diarrhea (n=3), thrombocytopenia (n=2), transaminitis (n=2), and rash (n=2). Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days), but none at 400mg + 100mg palbo. The combination of ipat and palbo demonstrated an additive effect in vitro, with increased sensitivity to lower doses of palbo in the presence of ipat. Based on the totality of data, 400mg ipat + 100mg palbo + fulv 500 mg was selected as the recommended phase II dose (RP2D) in the post-CDK4/6i setting. Conclusions: The triplet combination of endocrine therapy with AKTi and lower dose CDK4/6i appears to be well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. Further study is needed to evaluate biomarkers associated with higher AKTi benefit in order to guide rational development of combination therapy for patients with HR+/HER2- MBC in the post-CDK4/6i setting. Overall, this translational study demonstrates how insight into the molecular mechanisms of CDK4/6i resistance and combinatorial modeling can be leveraged to develop actionable therapeutic regimens for patients with MBC.

Citation Format: Seth A. Wander, Douglas S. Micalizzi, Taronish Dubash, Dejan Juric, Laura M. Spring, Neelima Vidula, Jennifer Keenan, Maureen Beeler, Elene Viscosi, Dante Che, Elizabeth L. Fisher, Rachel A. Hepp, Beverly Moy, Steven J. Isakoff, Leif W. Ellisen, Jeffrey G. Supko, Shyamala Maheswaran, Daniel A. Haber, Aditya Bardia. AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-22.

Abstract P3-23-02: Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer receiving CDK 4/6 inhibitors

Background: CDK 4/6 inhibitors have transformed the landscape of breast oncology. A CDK 4/6 inhibitor in combination with endocrine therapy is recommended as 1st line therapy for patients with metastatic hormone receptor positive breast cancer. CDK 4/6 inhibitors have purported immunomodulatory effects and while effective, myelosuppression is a common adverse effect of CDK 4/6 inhibitor treatment of breast cancer. The impact of CDK 4/6 inhibitor therapy on immunogenicity of vaccines is not known. In this study, we evaluated the spike antibody response to SARS-CoV-2 vaccines among patients with breast cancer receiving endocrine therapy with or without CDK 4/6 inhibitors.Methods: In the Cancer COVID and Vaccine (CANVAX) study eligible patients included patients with breast cancer who had completed all scheduled doses of SARS-CoV-2 vaccines. Chart review was conducted to identify patients who had received endocrine therapy with or without CDK 4/6 inhibitor. We used validated assays to measure anti-SARS-CoV-2 total IgA/M/G spike antibodies and virus neutralization. We evaluated the magnitude of antibody response based on geometric mean concentrations (GMCs) as well as the % of patients with inadequate seroconversion (defined as levels &lt;100 U/ml). Independent T-test based on log-transformed antibody values was utilized to compare the spike antibody levels and p value of ≤ 0.05 was considered statistically significant.Results: Between April 2021 and June 2021, 203 patients with breast cancer were enrolled. As of the cut-off date (2nd July 2021), results were available for 73 patients treated with endocrine therapy alone (N = 23), or with CDK 4/6 inhibitor-based therapy (N = 50). Most were females (98.6%), white (83.6%), and had metastatic breast cancer (68.5%). 49.3% had received BNT162b2 (Pfizer), 37% mRNA1273 (Moderna), and 13.7% Ad26.COV2.S (Johnson and Johnson/Janssen) vaccines. Overall, the mean spike antibody levels were similar between patients treated with endocrine therapy alone vs CDK 4/6 inhibitor-based therapy (GMC: 326 vs. 719 U/mL; p=0.704). Mean spike antibody levels were higher in patients with early breast cancer vs. metastatic breast cancer (GMC: 555 vs. 465 U/mL; p=0.031). However, patients who received Ad26.COV2.S had lower levels of mean spike antibody levels (GMC 47 U/ml), compared with patients treated with BNT162b2 (GMC 400 U/ml) or mRNA1273 (GMC 2203 U/mL; P&lt;0.01 for both comparisons). Comparison of neutralization titers in 66 individuals supported the above results. 11 (15.1%) patients had low antibody titers (&lt;100U/ml) of seroconversion and 3 received a booster vaccine, with 1 having available repeat titer results thus far demonstrating a significant improvement.Conclusions: The majority of patients receiving CDK 4/6 inhibitor have adequate antibody response to SARS-CoV-2 vaccines, particularly mRNA vaccines. However, a minority of patients may require booster vaccine to augment immunity. Monitoring spike antibody levels could be helpful to identify patients with inadequate seroconversion and guide mitigation strategies for patients with breast cancer.

Citation Format: Elyssa Denault, Erika Nakajima, Vivek Naranbhai, Alejandro Balazs, Lindsey Mortensen, Elizabeth Niehoff, Caroline Barabell, Jennifer A. Hutchinson, Seth A. Wander, Aron S. Rosenstock, Leif W. Ellisen, Beverly Moy, Steven J. Isakoff, Justin F. Gainor, A. John Iafrate, Aditya Bardia, Laura M. Spring. Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer receiving CDK 4/6 inhibitors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-23-02.

Abstract P1-14-02: Phase II study of adjuvant endocrine therapy with CDK 4/6 inhibitor, ribociclib, for localized ER+/HER2- breast cancer (LEADER, part 1)

Background: CDK 4/6 inhibitors have demonstrated substantial efficacy in treating ER+/HER2- metastatic breast cancer. Therefore, there is great interest in exploring their ability to reduce recurrence risk in early breast cancer. However, conflicting results were observed in the large adjuvant phase 3 clinical trials investigating combination of endocrine therapy and CDK 4/6 inhibitor (PALLAS, MONARCH-E). While these adjuvant clinical trials evaluated upfront use of CDK 4/6 inhibitor, the optimal timing of adding CDK 4/6 inhibitor for HR+/HER2- breast cancer remains unknown. We conducted a prospective phase II clinical trial to evaluate the addition of a CDK 4/6 inhibitor, ribociclib, in patients who were already on adjuvant endocrine therapy. Methods: In part 1 of the clinical trial, eligibility included patients with localized stage I-III ER+ (≥ 10%), HER2- breast cancer; completed surgery; and were on adjuvant endocrine therapy (any number of years) with at least one year or more of treatment remaining. Patients were randomized to two different ribociclib schedules: continuous (400 mg daily of 28-day cycle; arm 1) or intermittent (600 mg daily on days 1-21 of 28-day cycle; arm 2) for one year. Patients were concurrently treated with an aromatase inhibitor (plus GnRH agonist if premenopausal). Tolerance was evaluated via CTCAE version 4.03 and proportion of subjects who discontinued CDK 4/6 treatment early. Stratification factors for statistical analysis included: disease stage (III vs lower), duration of prior endocrine therapy (within 2 years; 2-5 years vs &gt; 5 years), and whether the patient received prior chemotherapy or not. Baseline characteristics and risk factors for recurrence and for early discontinuation were compared between the arms of the study using Pearson's chi-squared test. Actuarial analysis of time to recurrence was done using the Kaplan-Meier estimator. The primary objective of part 1 was to estimate adherence to ribociclib treatment in the adjuvant setting. Results: In total, 81 patients were enrolled between February 2018 and September 2019, and 25 (31%) discontinued ribociclib treatment early, with no significant difference between study arms. The most common grade 3 or greater adverse events (AEs) leading to study discontinuation were neutropenia (44%), alanine aminotransferase increase (28%), and aspartate aminotransferase increase (16%). Among patients who discontinued early, neutropenia was more frequent in the 600 mg arm, 9 of 12 patients (75%), versus 2 of 13 patients (15%) in the 400 mg arm. No patients discontinued early due to prolonged QTc. Ribociclib was dose reduced for 22 patients (27%), with no significant difference between study arms (p = 0.12). After a median follow-up of 20 months, two patients have experienced disease recurrence with recurrence-free survival of 100% at 1 year and 97% (95% CI 88-99%) at 2 years. Biomarker (ctDNA) results will be reported at the meeting. Conclusions: Results demonstrate that while serious AEs with one year of adjuvant ribociclib are low, a substantial number of patients discontinued adjuvant CDK 4/6 inhibitor within 1 year. Overall, with limited follow-up, only two patients had recurrent disease since completion of ribociclib treatment. Tolerability and identifying patient subsets who will most benefit need to be carefully considered with CDK 4/6 inhibitors in the adjuvant setting.

Citation Format: Laura M Spring, Lauren Scarpetti, Andrzej Niemierko, Steven J Isakoff, Beverly Moy, Seth A Wander, Elisabeth Smith, Elizabeth Abraham, Jennifer Shin, Jaymin M Patel, Amy Comander, Therese Mulvey, Aditya Bardia. Phase II study of adjuvant endocrine therapy with CDK 4/6 inhibitor, ribociclib, for localized ER+/HER2- breast cancer (LEADER, part 1) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-14-02.

Immunogenicity and Reactogenicity of SARS-CoV-2 Vaccines in Patients With Cancer: The CANVAX Cohort Study

PURPOSE

The immunogenicity and reactogenicity of SARS-CoV-2 vaccines in patients with cancer are poorly understood.

METHODS

We performed a prospective cohort study of adults with solid-organ or hematologic cancers to evaluate anti-SARS-CoV-2 immunoglobulin A/M/G spike antibodies, neutralization, and reactogenicity ≥ 7 days following two doses of mRNA-1273, BNT162b2, or one dose of Ad26.COV2.S. We analyzed responses by multivariate regression and included data from 1,638 healthy controls, previously reported, for comparison.

RESULTS

Between April and July 2021, we enrolled 1,001 patients; 762 were eligible for analysis (656 had neutralization measured). mRNA-1273 was the most immunogenic (log10 geometric mean concentration [GMC] 2.9, log10 geometric mean neutralization titer [GMT] 2.3), followed by BNT162b2 (GMC 2.4; GMT 1.9) and Ad26.COV2.S (GMC 1.5; GMT 1.4; P < .001). The proportion of low neutralization (< 20% of convalescent titers) among Ad26.COV2.S recipients was 69.9%. Prior COVID-19 infection (in 7.1% of the cohort) was associated with higher responses (P < .001). Antibody titers and neutralization were quantitatively lower in patients with cancer than in comparable healthy controls, regardless of vaccine type (P < .001). Receipt of chemotherapy in the prior year or current steroids were associated with lower antibody levels and immune checkpoint blockade with higher neutralization. Systemic reactogenicity varied by vaccine and correlated with immune responses (P = .002 for concentration, P = .016 for neutralization). In 32 patients who received an additional vaccine dose, side effects were similar to prior doses, and 30 of 32 demonstrated increased antibody titers (GMC 1.05 before additional dose, 3.17 after dose).

CONCLUSION

Immune responses to SARS-CoV-2 vaccines are modestly impaired in patients with cancer. These data suggest utility of antibody testing to identify patients for whom additional vaccine doses may be effective and appropriate, although larger prospective studies are needed.

Mechanisms of Resistance to CDK4/6 Blockade in Advanced Hormone Receptor-positive, HER2-negative Breast Cancer and Emerging Therapeutic Opportunities

The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have become the standard of care, in combination with antiestrogen therapy, for patients with hormone receptor-positive (HR⁺)/HER2^- advanced breast cancer. Various preclinical and translational research efforts have begun to shed light on the genomic and molecular landscape of resistance to these agents. Drivers of resistance to CDK4/6i therapy can be broadly subdivided into alterations impacting cell-cycle mediators and activation of oncogenic signal transduction pathways. The resistance drivers with the best translational evidence supporting their putative role have been identified via next-generation sequencing of resistant tumor biopsies in the clinic and validated in laboratory models of HR⁺ breast cancer. Despite the diverse landscape of resistance, several common, therapeutically actionable resistance nodes have been identified, including the mitotic spindle regulator Aurora Kinase A, as well as the AKT and MAPK signaling pathways. Based upon these insights, precision-guided therapeutic strategies are under active clinical development. This review will highlight the emerging evidence, in the clinic and in the laboratory, implicating this diverse spectrum of molecular resistance drivers.

Antibody drug conjugates for patients with breast cancer

The receptor-based classification of breast cancer predicts its optimal therapy. Hormone Receptor (HR) positive breast cancer is treated with endocrine therapy, and HER2+ disease is treated with HER2-targeted therapy. Triple negative breast cancer (TNBC), defined as tumors lacking HR and HER2, represents an aggressive subtype of breast cancer associated with poor prognosis. Development of targeted therapy for this subtype has been challenging since TNBC usually lacks targetable genomic alterations. However, the advent of antibody drug conjugates (ADC) to target antigens overexpressed in breast cancer has opened the door to a new class of breast cancer therapeutics. In this review, we describe the current FDA-approved ADC therapies for breast cancer, including sacituzumab govitecan, as well as agents currently in advanced stages of investigation. In addition, we review the potential therapeutic application of ADCs across different breast cancer subtypes. In the future, therapeutic advances in ADCs targeting different antigens could redefine the current receptor-based classification of breast cancer.

Impact of HER2 Heterogeneity on Treatment Response of Early-Stage HER2-Positive Breast Cancer: Phase II Neoadjuvant Clinical Trial of T-DM1 Combined with Pertuzumab

Intratumor heterogeneity is postulated to cause therapeutic resistance. To prospectively assess the impact of HER2 (ERBB2) heterogeneity on response to HER2-targeted therapy, we treated 164 patients with centrally confirmed HER2-positive early-stage breast cancer with neoadjuvant trastuzumab emtansine plus pertuzumab. HER2 heterogeneity was assessed on pretreatment biopsies from two locations of each tumor. HER2 heterogeneity, defined as an area with ERBB2 amplification in >5% but <50% of tumor cells, or a HER2-negative area by FISH, was detected in 10% (16/157) of evaluable cases. The pathologic complete response rate was 55% in the nonheterogeneous subgroup and 0% in the heterogeneous group (P < 0.0001, adjusted for hormone receptor status). Single-cell ERBB2 FISH analysis of cellular heterogeneity identified the fraction of ERBB2 nonamplified cells as a driver of therapeutic resistance. These data suggest HER2 heterogeneity is associated with resistance to HER2-targeted therapy and should be considered in efforts to optimize treatment strategies. SIGNIFICANCE: HER2-targeted therapies improve cure rates in HER2-positive breast cancer, suggesting chemotherapy can be avoided in a subset of patients. We show that HER2 heterogeneity, particularly the fraction of ERBB2 nonamplified cancer cells, is a strong predictor of resistance to HER2 therapies and could potentially be used to optimize treatment selection.See related commentary by Okines and Turner, p. 2369.This article is highlighted in the In This Issue feature, p. 2355.

Systematic tissue collection during clinical breast biopsy is feasible, safe and enables high-content translational analyses

Systematic collection of fresh tissues for research at the time of diagnostic image-guided breast biopsy has the potential to fuel a wide variety of innovative studies. Here we report the initial experience, including safety, feasibility, and laboratory proof-of-principle, with the collection and analysis of research specimens obtained via breast core needle biopsy immediately following routine clinical biopsy at a single institution over a 14-month period. Patients underwent one or two additional core biopsies following collection of all necessary clinical specimens. In total, 395 patients were approached and 270 consented to the research study, yielding a 68.4% consent rate. Among consenting patients, 238 lesions were biopsied for research, resulting in 446 research specimens collected. No immediate complications were observed. Representative research core specimens showed high diagnostic concordance with clinical core biopsies. Flow cytometry demonstrated consistent recovery of hundreds to thousands of viable cells per research core. Among a group of HER2 + tumor research specimens, HER2 assessment by flow cytometry correlated highly with immunohistochemistry (IHC) staining, and in addition revealed extensive inter- and intra-tumoral variation in HER2 levels of potential clinical relevance. Suitability for single-cell transcriptomic analysis was demonstrated for a triple-negative tumor core biopsy, revealing substantial cellular diversity in the tumor immune microenvironment, including a prognostically relevant T cell subpopulation. Thus, collection of fresh tissues for research purposes at the time of diagnostic breast biopsy is safe, feasible and efficient, and may provide a high-yield mechanism to generate a rich tissue repository for a wide variety of cross-disciplinary research.

ESR1 mutation as an emerging clinical biomarker in metastatic hormone receptor-positive breast cancer

In metastatic hormone receptor-positive breast cancer, ESR1 mutations are a common cause of acquired resistance to the backbone of therapy, estrogen deprivation by aromatase inhibition. How these mutations affect tumor sensitivity to established and novel therapies are active areas of research. These therapies include estrogen receptor-targeting agents, such as selective estrogen receptor modulators, covalent antagonists, and degraders (including tamoxifen, fulvestrant, and novel agents), and combination therapies, such as endocrine therapy plus CDK4/6, PI3K, or mTORC1 inhibition. In this review, we summarize existing knowledge surrounding the mechanisms of action of ESR1 mutations and roles in resistance to aromatase inhibition. We then analyze the recent literature on how ESR1 mutations affect outcomes in estrogen receptor-targeting and combination therapies. For estrogen receptor-targeting therapies such as tamoxifen and fulvestrant, ESR1 mutations cause relative resistance in vitro but do not clearly lead to resistance in patients, making novel agents in this category promising. Regarding combination therapies, ESR1 mutations nullify any aromatase inhibitor component of the combination. Thus, combinations using endocrine alternatives to aromatase inhibition, or combinations where the non-endocrine component is efficacious as monotherapy, are still effective against ESR1 mutations. These results emphasize the importance of investigating combinatorial resistance, challenging as these efforts are. We also discuss future directions and open questions, such as studying the differences among distinct ESR1 mutations, asking how to adjust clinical decisions based on molecular surveillance testing, and developing novel therapies that are effective against ESR1 mutations.

Phase 1b clinical trial of ado-trastuzumab emtansine and ribociclib for HER2-positive metastatic breast cancer

Patients with HER2+ metastatic breast cancer are often treated with a multitude of therapies in the metastatic setting, and additional strategies to prolong responses to anti-HER2 therapies are needed. Preclinical evidence suggests synergy between cyclin-dependent kinase 4 and 6 (CDK 4/6) inhibitors and anti-HER2 therapies. We conducted a phase 1b study of ribociclib and ado-trastuzumab emtansine (T-DM1) in patients with advanced/metastatic HER2-positive breast cancer previously treated with trastuzumab and a taxane in any setting, with four or fewer prior lines of therapy in the metastatic setting. A standard 3 + 3 dose-escalation design was used to evaluate various doses of ribociclib in combination with T-DM1, starting at 300 mg. The primary objective was to determine the maximum tolerated dose and/or recommended phase 2 dose (RP2D) of ribociclib in combination with T-DM1. A total of 12 patients were enrolled. During dose-escalation, patients received doses of ribociclib of 300 mg (n = 3), 400 mg (n = 3), 500 mg (n = 3), and 600 mg (n = 3). No dose-limiting toxicities were observed. The majority of toxicities were Grade 1 and 2, and the most common Grade 3 toxicities were neutropenia (33%), leukopenia (33%), and anemia (25%). After a median follow-up of 12.4 months, the median PFS was 10.4 months (95% confidence interval, 2.7-19.3). Based on the pharmacokinetic analysis, adverse events, and dose reductions, 400 mg was determined to be the RP2D for ribociclib given on days 8-21 of a 21-day cycle with T-DM1.

Locally Recurrent Secretory Carcinoma of the Breast with NTRK3 Gene Fusion

Enhanced understanding of the molecular events underlying oncogenesis has led to the development of "tumor-agnostic" treatment strategies, which aim to target a tumor's genomic profile regardless of its anatomic site of origin. A classic example is the translocation resulting in an ETV6-NTRK3 gene fusion, a characteristic driver of a histologically diverse array of cancers. The chimeric ETV6-NTRK3 fusion protein elicits constitutive activation of the tropomyosin receptor kinase (TRK) C protein, leading to increased cell survival, growth, and proliferation. Two TRK inhibitors, larotrectinib and entrectinib, are currently approved for use in the metastatic setting for the treatment of advanced solid tumors harboring NTRK fusions. Here we report a rare case of recurrent secretory carcinoma of the breast (SCB) with NTRK3 gene fusion. Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case detailed here is the first to the authors' knowledge of recurrence within 1 year of surgery. We review the molecular findings and potential clinical significance. KEY POINTS: The translocation resulting in the ETV6-NTRK3 gene fusion is a known oncogenic driver characteristic of secretory carcinoma of the breast (SCB). Whereas most cases of SCB represent slow-growing tumors with favorable outcomes, the case here with ETV6-NTRK3 gene fusion had local recurrence within 1 year of surgery. Two tropomyosin receptor kinase (TRK) inhibitors, larotrectinib and entrectinib, are approved to treat NTRK fusion-positive tumors, demonstrating sustained high overall response rates in the metastatic setting. Approval of TRK inhibitors necessitates optimization of NTRK fusion detection assays, including detection with liquid biopsies.

Sacituzumab Govitecan for Metastatic Triple-Negative Breast Cancer: Clinical Overview and Management of Potential Toxicities

Patients with metastatic triple-negative breast cancer have a poor prognosis. Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate that contains the irinotecan active metabolite, SN-38, linked to a humanized monoclonal antibody targeting trophoblast cell surface antigen 2, which is overexpressed in many solid tumors. In a basket design phase I/II study, sacituzumab govitecan demonstrated promising single-agent therapeutic activity in multiple cancer cohorts, leading to accelerated approval by the U.S. Food and Drug Administration of sacituzumab govitecan-hziy (TRODELVY) for the treatment of patients with metastatic triple-negative breast cancer who had received at least two prior therapies in the metastatic setting. Recently, results of the phase III trial, ASCENT, were confirmatory. There is limited available information on the adverse event management with sacituzumab govitecan needed to maximize the dose and duration of effective therapy while maintaining patient quality of life. This review summarizes the clinical development and the practical management of patients receiving sacituzumab govitecan. Sacituzumab govitecan has a well-defined and manageable toxicity profile, and rapid recognition and appropriate early and proactive management will allow clinicians to optimize sacituzumab govitecan treatment for patients. IMPLICATIONS FOR PRACTICE: Sacituzumab govitecan (TRODELVY) is a novel antibody-drug conjugate composed of the active metabolite of irinotecan (SN-38) conjugated to a monoclonal antibody targeting trophoblast cell surface antigen 2, an epithelial cell surface antigen overexpressed in many cancers. Because of the rapid approval of sacituzumab govitecan, there is limited available information on adverse event (AE) management with this agent. As such, this article reviews the clinical development of the drug, the AE profile, and provides recommendations regarding AE management to help optimize therapy with sacituzumab govitecan.