Overcoming BRAF and CDK4/6 inhibitor resistance by inhibiting MAP3K3-dependent protection against YAP lysosomal degradation

Transcriptional programs governed by YAP play key roles in conferring resistance to various molecular-targeted anticancer agents. Strategies aimed at inhibiting YAP activity have garnered substantial interest as a means to overcome drug resistance. However, despite extensive research into the canonical Hippo-YAP pathway, few clinical agents are currently available to counteract YAP-associated drug resistance. Here, we present a novel mechanism of YAP stability regulation by MAP3K3 that is independent of Hippo kinases. Furthermore, we identified MAP3K3 as a target for overcoming anticancer drug resistance. Depletion of MAP3K3 led to a substantial reduction in the YAP protein level in melanoma and breast cancer cells. Mass spectrometry analysis revealed that MAP3K3 phosphorylates YAP at serine 405. This MAP3K3-mediated phosphorylation event hindered the binding of the E3 ubiquitin ligase FBXW7 to YAP, thereby preventing its p62-mediated lysosomal degradation. Robust YAP activation was observed in CDK4/6 inhibitor-resistant luminal breast cancer cells. Knockdown or pharmacological inhibition of MAP3K3 effectively suppressed YAP activity and restored CDK4/6 inhibitor sensitivity. Similarly, elevated MAP3K3 expression supported the prosurvival activity of YAP in BRAF inhibitor-resistant melanoma cells. Inhibition of MAP3K3 decreased YAP-dependent cell proliferation and successfully restored BRAF inhibitor sensitivity. In conclusion, our study reveals a previously unrecognized mechanism for the regulation of YAP stability, suggesting MAP3K3 inhibition as a promising strategy for overcoming resistance to CDK4/6 and BRAF inhibitors in cancer treatment.

Giredestrant for Estrogen Receptor-Positive, HER2-Negative, Previously Treated Advanced Breast Cancer: Results From the Randomized, Phase II acelERA Breast Cancer Study

PURPOSE

To compare giredestrant and physician's choice of endocrine monotherapy (PCET) for estrogen receptor-positive, HER2-negative, advanced breast cancer (BC) in the phase II acelERA BC study (ClinicalTrials.gov identifier: NCT04576455).

METHODS

Post-/pre-/perimenopausal women, or men, age 18 years or older with measurable disease/evaluable bone lesions, whose disease progressed after 1-2 lines of systemic therapy (≤1 targeted, ≤1 chemotherapy regimen, prior fulvestrant allowed) were randomly assigned 1:1 to giredestrant (30 mg oral once daily) or fulvestrant/aromatase inhibitor per local guidelines (+luteinizing hormone-releasing hormone agonist in pre-/perimenopausal women, and men) until disease progression/unacceptable toxicity. Stratification was by visceral versus nonvisceral disease, prior cyclin-dependent kinase 4/6 inhibitor, and prior fulvestrant. The primary end point was investigator-assessed progression-free survival (INV-PFS).

RESULTS

At clinical cutoff (February 18, 2022; median follow-up: 7.9 months; N = 303), the INV-PFS hazard ratio (HR) was 0.81 (95% CI, 0.60 to 1.10; P = .1757). In the prespecified secondary end point analysis of INV-PFS by ESR1 mutation (m) status in circulating tumor DNA-evaluable patients (n = 232), the HR in patients with a detectable ESR1m (n = 90) was 0.60 (95% CI, 0.35 to 1.03) versus 0.88 (95% CI, 0.54 to 1.42) in patients with no ESR1m detected (n = 142). Related grade 3-4 adverse events (AEs), serious AEs, and discontinuations due to AEs were balanced across arms.

CONCLUSION

Although the acelERA BC study did not reach statistical significance for its primary INV-PFS end point, there was a consistent treatment effect with giredestrant across most key subgroups and a trend toward favorable benefit among patients with ESR1-mutated tumors. Giredestrant was well tolerated, with a safety profile comparable to PCET and consistent with known endocrine therapy risks. Overall, these data support the continued investigation of giredestrant in other studies.

TROPION-Breast01: Datopotamab deruxtecan vs chemotherapy in pre-treated inoperable or metastatic HR+/HER2- breast cancer

Improving the prognosis for patients with metastatic HR+/HER2- breast cancer remains an unmet need. Patients with tumors that have progressed on endocrine therapy and/or are not eligible for endocrine therapy had limited treatment options beyond chemotherapy. Antibody-drug conjugates are a novel and promising treatment class in this setting. Datopotamab deruxtecan (Dato-DXd) consists of a TROP2-directed humanized IgG1 monoclonal antibody attached via a serum-stable cleavable linker to a topoisomerase I inhibitor payload. TROPION-Breast01 is an ongoing phase III study that is evaluating the efficacy and safety of Dato-DXd compared with investigator's choice of standard-of-care chemotherapy in patients with inoperable or metastatic HR+/HER2- breast cancer who have received one or two prior lines of systemic chemotherapy in the inoperable or metastatic setting. Clinical Trial Registration: NCT05104866 (ClinicalTrials.gov).

Trastuzumab deruxtecan in previously treated patients with HER2-positive metastatic breast cancer: updated survival results from a phase II trial (DESTINY-Breast01)

BACKGROUND

Primary analysis of the multicenter, open-label, single-arm, phase II DESTINY-Breast01 trial (median follow-up 11.1 months) demonstrated durable antitumor activity with trastuzumab deruxtecan (T-DXd) in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) previously treated with trastuzumab emtansine (T-DM1). We report updated cumulative survival outcomes with a median follow-up of 26.5 months (data cut-off 26 March 2021).

PATIENTS AND METHODS

Patients with HER2-positive mBC resistant or refractory to T-DM1 received T-DXd 5.4 mg/kg intravenously every 3 weeks until disease progression, unacceptable adverse events, or withdrawal of consent. The primary endpoint was confirmed objective response rate (ORR) by independent central review (ICR). Secondary endpoints included overall survival (OS), duration of response (DoR), progression-free survival (PFS), and safety.

RESULTS

The ORR by ICR was 62.0% [95% confidence interval (CI) 54.5% to 69.0%] in patients who received T-DXd 5.4 mg/kg every 3 weeks (n = 184). Median OS was 29.1 months (95% CI 24.6-36.1 months). Median PFS and DoR were 19.4 months (95% CI 14.1-25.0 months) and 18.2 months (95% CI 15.0 months-not evaluable), respectively. Drug-related treatment-emergent adverse events (TEAEs) were observed in 183 patients (99.5%), and 99 patients (53.8%) had one or more grade ≥3 TEAEs. Adjudicated drug-related interstitial lung disease/pneumonitis occurred in 15.8% of patients (n = 29), of which 2.7% (n = 5) were grade 5.

CONCLUSIONS

These updated results provide further evidence of sustained antitumor activity of T-DXd with a consistent safety profile in heavily pretreated patients with HER2-positive mBC.

Phase Ia/b Study of Giredestrant ± Palbociclib and ± Luteinizing Hormone-Releasing Hormone Agonists in Estrogen Receptor-Positive, HER2-Negative, Locally Advanced/Metastatic Breast Cancer

PURPOSE

Giredestrant is an investigational next-generation, oral, selective estrogen receptor antagonist and degrader for the treatment of estrogen receptor-positive (ER+) breast cancer. We present the primary analysis results of the phase Ia/b GO39932 study (NCT03332797).

PATIENTS AND METHODS

Patients with ER+, HER2-negative locally advanced/metastatic breast cancer previously treated with endocrine therapy received single-agent giredestrant (10, 30, 90, or 250 mg), or giredestrant (100 mg) ± palbociclib 125 mg ± luteinizing hormone-releasing hormone (LHRH) agonist. Detailed cardiovascular assessment was conducted with giredestrant 100 mg. Endpoints included safety (primary), pharmacokinetics, pharmacodynamics, and efficacy.

RESULTS

As of January 28, 2021, with 175 patients enrolled, no dose-limiting toxicity was observed, and the MTD was not reached. Adverse events (AE) related to giredestrant occurred in 64.9% and 59.4% of patients in the single-agent ± LHRH agonist and giredestrant + palbociclib ± LHRH agonist cohorts, respectively (giredestrant-only-related grade 3/4 AEs were reported in 4.5% of patients across the single-agent cohorts and 3.1% of those with giredestrant + palbociclib). Dose-dependent asymptomatic bradycardia was observed, but no clinically significant changes in cardiac-related outcomes: heart rate, blood pressure, or exercise duration. Clinical benefit was observed in all cohorts (48.6% of patients in the single-agent cohort and 81.3% in the giredestrant + palbociclib ± LHRH agonist cohort), with no clear dose relationship, including in patients with ESR1-mutated tumors.

CONCLUSIONS

Giredestrant was well tolerated and clinically active in patients who progressed on prior endocrine therapy. Results warrant further evaluation of giredestrant in randomized trials in early- and late-stage ER+ breast cancer.

A nationwide real-world study for evaluation of effectiveness and safety of T-DM1 in patients with HER2-positive metastatic breast cancer in Korea (KCSG BR19-15)

Purpose

This study aimed to investigate clinical practices and factors related to the outcomes of T-DM1 use in patients with HER2-positive metastatic breast cancer (mBC).

Methods

We included patients with HER2-positive mBC who received T-DM1 as a palliative therapy between August 2017 and December 2018. The safety and outcomes of T-DM1, including overall response rate (ORR), progression-free survival (PFS), and overall survival (OS), were evaluated. A Cox proportional hazards model was used to estimate the hazard ratio and 95% confidence interval (CI) for mortality or progression to HER2-positive mBC.

Results

In total, 824 patients were enrolled during the study period. The mean age of patients was 58 years, and 516 (62.6%) patients relapsed after curative treatment. Excluding a history of endocrine therapy, 341 (41.4%) patients previously received none or first-line chemotherapy, 179 (21.7%) received second-line therapy, and 303 (36.9%) received third-or later-line chemotherapy before T-DM1 therapy. During a median follow-up of 16.8 months, the ORR was 35%, the median PFS was 6.6 months, and the median OS was not reached. The clinical factors associated with the hazard of progression were age (<65 years), poor performance status (⩾2), advanced line of palliative chemotherapy (⩾2), prior pertuzumab use, and treatment duration of palliative trastuzumab (<10 months). Common grade 3-4 adverse events were thrombocytopenia (n = 107, 13.2%), neutropenia (n = 23, 2.8%), anemia (n = 21, 2.6%), and elevated liver enzyme (n = 20, 2.5%). Hypokalemia (⩽3.0 mmol/L) and any-grade bleeding events occurred in 25 (3.1%) and 94 (22.6%) patients, respectively.

Conclusion

This is the first nationwide real-world study of T-DM1 use in patients with HER2-positive mBC in Korea. The effectiveness and toxicity profiles of T-DM1 in real-world practice were comparable to those in randomized trials. Moreover, patient factors and previous anti-HER2 therapy could predict the outcomes of T-DM1 therapy.

Pemetrexed plus vinorelbine versus vinorelbine monotherapy in patients with metastatic breast cancer (KCSG-BR15-17): A randomized, open-label, multicenter, phase II trial

INTRODUCTION

Metastatic breast cancer refractory to anthracycline and taxanes often shows rapid progression. The development of effective and tolerable combination regimens for these patients is needed. This phase II trial investigated the efficacy of pemetrexed plus vinorelbine in patients with metastatic breast cancer.

METHODS

This randomized, open-label, phase II trial was conducted in 17 centers in Korea. Patients with advanced breast cancer who had previously been treated with anthracyclines and taxanes were randomly assigned in a 1:1 ratio to receive either vinorelbine or pemetrexed plus vinorelbine. Randomization was stratified by prior capecitabine treatment and hormone receptor status. The primary endpoint was investigator-assessed progression-free survival (PFS). Secondary endpoints included the objective response rate, overall survival, safety, and quality of life.

RESULTS

Between March 2017 and August 2019, a total of 125 patients were enrolled. After a median follow-up duration of 14.1 months, 118 progression events and 88 death events had occurred. Sixty-two patients were assigned to the pemetrexed plus vinorelbine arm, and 63 were assigned to the vinorelbine arm. Pemetrexed plus vinorelbine significantly prolonged PFS compared to vinorelbine (5.7 vs. 1.5 months, p < 0.001). The combination arm had higher disease control rate (76.8% vs. 45.9%, p = 0.001) and a tendency toward longer overall survival (16.8 vs. 10.5 months, p = 0.102). Anemia was more frequent in the pemetrexed plus vinorelbine arm per cycle compared with vinorelbine (7.9% vs. 1.9%, p < 0.001), but there was no difference in the incidence of grade 3-4 neutropenia per cycle between the pemetrexed plus vinorelbine arm and the vinorelbine single arm (14.7% vs. 19.5%, p = 0.066).

CONCLUSIONS

This phase II study showed that pemetrexed plus vinorelbine led to a longer PFS than vinorelbine. Adverse events of pemetrexed plus vinorelbine were generally manageable.

Clinical activity of nivolumab in combination with eribulin in HER2-negative metastatic breast cancer: A phase IB/II study (KCSG BR18-16)

AIM

We evaluated the efficacy and safety of nivolumab and eribulin combination therapy for metastatic breast cancer (BC) in Asian populations.

METHODS

In this parallel phase II study, adult patients with histologically confirmed recurrent/metastatic hormone receptor-positive/HER2-negative (HR+HER2-) or triple-negative BC (TNBC) were prospectively enroled from 10 academic hospitals in Korea (ClinicalTrials.gov Identifier: NCT04061863). They received nivolumab (360 mg) on day 1 plus eribulin (1.4 mg/m2) on days 1 and 8 every 3 weeks until disease progression or intolerable toxicity. The primary endpoint was the investigator-assessed 6-month progression-free survival (PFS) rate in each subtype. Secondary endpoints included investigator-assessed objective response rate (ORR) as per Response Evaluation Criteria in Advanced Solid Tumors version 1.1, disease control rate, overall survival, and treatment toxicity. The association between PD-L1 expression and efficacy was investigated.

RESULTS

Forty-five patients with HR+HER2- BC and 45 with TNBC were enroled. Their median age was 51 (range, 31-71) years, and 74 (82.2%) received one or two prior treatments before enrolment. Six-month PFS was 47.2% and 25.1% in the HR+HER2- and TNBC cohorts, respectively. Median PFS was 5.6 (95% confidence interval [CI]: 5.3-7.4) and 3.0 (95% CI: 2.1-5.2) months in the HR+HER2- and TNBC groups, respectively. ORRs were 53.3% (complete response [CR]: 0, partial response [PR]: 24) and 28.9% (CR: 1, PR: 12). Patients with PD-L1+ tumours (PD-L1 expression ≥1%) and PD-L1- tumours (ORR 50% versus 53.8% in HR+HER2-, 30.8% versus 29.0% in TNBC) had similar ORRs. Neutropenia was the most common grade 3/4 adverse event; the most common immune-related adverse events (AEs) were grades 1/2 hypothyroidism and pruritus. Five patients discontinued therapy because of immune-related AEs.

CONCLUSION

Nivolumab plus eribulin showed promising efficacy and tolerable safety in previously treated HER2- metastatic BC.

TRIAL REGISTRATION

NCT04061863.

Targeting PEG10 as a novel therapeutic approach to overcome CDK4/6 inhibitor resistance in breast cancer

BACKGROUND

Breast cancer is the global leading cancer burden in women and the hormone receptor-positive (HR+) subtype is a major part of breast cancer. Though cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are highly effective therapy for HR+ subtype, acquired resistance is inevitable in most cases. Herein, we investigated the paternally expressed gene 10 (PEG10)-associated mechanism of acquired resistance to CDK4/6 inhibitors.

METHODS

Palbociclib-resistant cells were generated by exposing human HR+ breast cancer cell lines to palbociclib for 7-9 months. In vitro mechanistic study and in vivo xenograft assay were performed. For clinical relevance, public mRNA microarray data sets of early breast cancer were analyzed and PEG10 immunohistochemical staining was performed using pre-CDK4/6 inhibitor tumor samples.

RESULTS

We observed that PEG10 was significantly upregulated in palbociclib-resistant cells. Ectopic overexpression of PEG10 in parental cells caused CDK4/6 inhibitor resistance and enhanced epithelial-mesenchymal transition (EMT). On the contrary, PEG10-targeting siRNA or antisense oligonucleotides (ASOs) combined with palbociclib synergistically inhibited proliferation of palbociclib-resistant cells and growth of palbociclib-resistant xenograft in mice and suppressed EMT as well. The mechanistic study confirmed that high PEG10 expression suppressed p21, a natural CDK inhibitor, and SIAH1, a post-translational degrader of ZEB1, augmenting CDK4/6 inhibitor resistance. Then PEG10 siRNA combined with palbociclib suppressed cell cycle progression and EMT via activating p21 and SIAH1, respectively. Consequently, combined PEG10 inhibition and palbociclib overcame CDK4/6 inhibitor resistance. Furthermore, high PEG10 expression was significantly associated with a shorter recurrence-free survival (RFS) based on public mRNA expression data. In pre-CDK4/6 inhibitor treatment tissues, PEG10 positivity by IHC also showed a trend toward a shorter progression-free survival (PFS) with CDK4/6 inhibitor. These results support clinical relevance of PEG10 as a therapeutic target.

CONCLUSIONS

We demonstrated a novel PEG10-associated mechanism of CDK4/6 inhibitor resistance. We propose PEG10 as a promising therapeutic target for overcoming PEG10-associated resistance to CDK4/6 inhibitors.

A Multicenter, Prospective, Observational Study to Evaluate Ethanol-Induced Symptoms in Patients Receiving Docetaxel Chemotherapy

PURPOSE

Several previous studies and case reports have reported ethanol-induced symptoms in patients receiving anticancer drugs containing ethanol. Most docetaxel formulations contain ethanol as a solvent. However, there are insufficient data on ethanol-induced symptoms when docetaxel-containing ethanol is administered. The primary purpose of this study was to investigate the frequency and pattern of ethanol-induced symptoms during and after docetaxel administration. The secondary purpose was to explore the risk factors for ethanol-induced symptoms.

MATERIALS AND METHODS

This was a prospective, multicenter, observational study. The participants filled out ethanol-induced symptom questionnaire on the day of chemotherapy and the following day.

RESULTS

Data from 451 patients were analyzed. The overall occurrence rate of ethanol-induced symptoms was 44.3% (200/451 patients). The occurrence rate of facial flushing was highest at 19.7% (89/451 patients), followed by nausea in 18.2% (82/451 patients), and dizziness in 17.5% (79/451 patients). Although infrequent, unsteady walking and impaired balance occurred in 4.2% and 3.3% of patients, respectively. Female sex, presence of underlying disease, younger age, docetaxel dose, and docetaxel-containing ethanol amount were significantly associated with the occurrence of ethanol-induced symptoms.

CONCLUSION

The occurrence of ethanol-induced symptoms was not low in patients receiving docetaxel-containing ethanol. Physicians need to pay more attention to the occurrence of ethanol-induced symptoms and prescribe ethanol-free or low-ethanol-containing formulations to high-risk patients.

Efficacy of Limited Dose Modifications for Palbociclib-Related Grade 3 Neutropenia in Hormone Receptor-Positive Metastatic Breast Cancer

PURPOSE

Frequent neutropenia hinders uninterrupted palbociclib treatment in patients with hormone receptor (HR)-positive breast cancer. We compared the efficacy outcomes in multicenter cohorts of patients with metastatic breast cancer (mBC) receiving palbociclib following conventional dose modification or limited modified schemes for afebrile grade 3 neutropenia.

MATERIALS AND METHODS

Patients with HR-positive, human epidermal growth factor receptor 2-negative mBC (n=434) receiving palbociclib with letrozole as first-line therapy were analyzed and classified based on neutropenia grade and afebrile grade 3 neutropenia management as follows: group 1 (maintained palbociclib dose, limited scheme), group 2 (dose delay or reduction, conventional scheme), group 3 (no afebrile grade 3 neutropenia event), and group 4 (grade 4 neutropenia event). The primary and secondary endpoints were progression-free survival (PFS) between groups 1 and 2 and PFS, overall survival, and safety profiles among all groups.

RESULTS

During follow-up (median 23.7 months), group 1 (2-year PFS, 67.9%) showed significantly longer PFS than did group 2 (2-year PFS, 55.3%; p=0.036), maintained across all subgroups, and upon adjustment of the factors. Febrile neutropenia occurred in one and two patients of group 1 and group 2, respectively, without mortality.

CONCLUSION

Limited dose modification for palbociclib-related grade 3 neutropenia may lead to longer PFS, without increasing toxicity, than the conventional dose scheme.

Copy number aberrations in circulating tumor DNA enables prognosis prediction and molecular characterization of breast cancer

BACKGROUND

Low-pass whole-genome sequencing (LP-WGS)-based circulating tumor DNA (ctDNA) analysis is a versatile tool for somatic copy number aberration (CNA) detection, and this study aims to explore its clinical implication in breast cancer.

METHODS

We analyzed LP-WGS ctDNA data from 207 metastatic breast cancer (MBC) patients to explore prognostic value of ctDNA CNA burden and validated it in 465 stage II-III triple-negative breast cancer (TNBC) patients who received neoadjuvant chemotherapy in phase III PEARLY trial (NCT02441933). The clinical implication of locus level LP-WGS ctDNA profiling was further evaluated.

RESULTS

We found that a high baseline ctDNA CNA burden predicts poor overall survival and progression-free survival of MBC patients. The post hoc analysis of the PEARLY trial showed that a high baseline ctDNA CNA burden predicted poor disease-free survival independent from pathologic complete response (pCR), validating its robust prognostic significance. The 24-month disease-free survival rate was 96.9% and 55.9% in [pCR(+) and low I-score] and [non-pCR and high I-score] patients, respectively. The locus-level ctDNA CNA profile classified MBC patients into 5 molecular clusters and revealed targetable oncogenic CNAs. LP-WGS ctDNA and in vitro analysis identified the BCL6 amplification as a resistance factor for CDK4/6 inhibitors. We estimated ctDNA-based homologous recombination deficiency status of patients by shallowHRD algorithm, which was highest in the TNBC and correlated with platinum-based chemotherapy response.

CONCLUSIONS

These results demonstrate LP-WGS ctDNA CNA analysis as an essential tool for prognosis prediction and molecular profiling. Particularly, ctDNA CNA burden can serve as a useful determinant for escalating or de-escalating (neo)adjuvant strategy in TNBC patients.

Retrospective study to estimate the prevalence and describe the clinicopathological characteristics, treatments received, and outcomes of HER2-low breast cancer

BACKGROUND

Approximately 80% of all breast cancers (BCs) are currently categorized as human epidermal growth factor receptor 2 (HER2)-negative [immunohistochemistry (IHC) 0, 1+, or 2+/in situ hybridization (ISH) negative]; approximately 60% of BCs traditionally categorized as HER2-negative express low levels of HER2. HER2-low (IHC 1+ or IHC 2+/ISH-) status became clinically actionable with approval of trastuzumab deruxtecan to treat unresectable/metastatic HER2-low BC. Greater understanding of patients with HER2-low disease is urgently needed.

PATIENTS AND METHODS

This global, multicenter, retrospective study (NCT04807595) included tissue samples from patients with confirmed HER2-negative unresectable/metastatic BC [any hormone receptor (HR) status] diagnosed from 2014 to 2017. Pathologists rescored HER2 IHC-stained slides as HER2-low (IHC 1+ or IHC 2+/ISH-) or HER2 IHC 0 after training on low-end expression scoring using Ventana 4B5 and other assays at local laboratories (13 sites; 10 countries) blinded to historical scores. HER2-low prevalence and concordance between historical scores and rescores were assessed. Demographics, clinicopathological characteristics, treatments, and outcomes were examined.

RESULTS

In rescored samples from 789 patients with HER2-negative unresectable/metastatic BC, the overall HER2-low prevalence was 67.2% (HR positive, 71.1%; HR negative, 52.8%). Concordance was moderate between historical and rescored HER2 statuses (81.3%; κ = 0.583); positive agreement was numerically higher for HER2-low (87.5%) than HER2 IHC 0 (69.9%). More than 30% of historical IHC 0 cases were rescored as HER2-low overall (all assays) and using Ventana 4B5. There were no notable differences between HER2-low and HER2 IHC 0 in patient characteristics, treatments received, or clinical outcomes.

CONCLUSIONS

Approximately two-thirds of patients with historically HER2-negative unresectable/metastatic BC may benefit from HER2-low-directed treatments. Our data suggest that HER2 reassessment in patients with historical IHC 0 scores may be considered to help optimize selection of patients for treatment. Further, accurate identification of patients with HER2-low BC may be achieved with standardized pathologist training.

Capivasertib in Hormone Receptor-Positive Advanced Breast Cancer

BACKGROUND

AKT pathway activation is implicated in endocrine-therapy resistance. Data on the efficacy and safety of the AKT inhibitor capivasertib, as an addition to fulvestrant therapy, in patients with hormone receptor-positive advanced breast cancer are limited.

METHODS

In a phase 3, randomized, double-blind trial, we enrolled eligible pre-, peri-, and postmenopausal women and men with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer who had had a relapse or disease progression during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor therapy. Patients were randomly assigned in a 1:1 ratio to receive capivasertib plus fulvestrant or placebo plus fulvestrant. The dual primary end point was investigator-assessed progression-free survival assessed both in the overall population and among patients with AKT pathway-altered (PIK3CA, AKT1, or PTEN) tumors. Safety was assessed.

RESULTS

Overall, 708 patients underwent randomization; 289 patients (40.8%) had AKT pathway alterations, and 489 (69.1%) had received a CDK4/6 inhibitor previously for advanced breast cancer. In the overall population, the median progression-free survival was 7.2 months in the capivasertib-fulvestrant group, as compared with 3.6 months in the placebo-fulvestrant group (hazard ratio for progression or death, 0.60; 95% confidence interval [CI], 0.51 to 0.71; P<0.001). In the AKT pathway-altered population, the median progression-free survival was 7.3 months in the capivasertib-fulvestrant group, as compared with 3.1 months in the placebo-fulvestrant group (hazard ratio, 0.50; 95% CI, 0.38 to 0.65; P<0.001). The most frequent adverse events of grade 3 or higher in patients receiving capivasertib-fulvestrant were rash (in 12.1% of patients, vs. in 0.3% of those receiving placebo-fulvestrant) and diarrhea (in 9.3% vs. 0.3%). Adverse events leading to discontinuation were reported in 13.0% of the patients receiving capivasertib and in 2.3% of those receiving placebo.

CONCLUSIONS

Capivasertib-fulvestrant therapy resulted in significantly longer progression-free survival than treatment with fulvestrant alone among patients with hormone receptor-positive advanced breast cancer whose disease had progressed during or after previous aromatase inhibitor therapy with or without a CDK4/6 inhibitor. (Funded by AstraZeneca and the National Cancer Institute; CAPItello-291 ClinicalTrials.gov number, NCT04305496.).

Ten-year survival of neoadjuvant dual HER2 blockade in patients with HER2-positive breast cancer

BACKGROUND

Dual anti-HER2-targeted therapy in breast cancer (BC) significantly increased the rate of pathological complete response (pCR) compared to single blockade when added to chemotherapy. However, limited data exist on the long-term impact on survival of the additional increase in pCR.

METHODS

Neoadjuvant lapatinib and/or trastuzumab treatment optimisation (NCT00553358) is an international, randomised, open-label, phase III study investigating the addition of lapatinib to chemotherapy plus trastuzumab in HER2-positive early BC. Ten-year event-free survival (EFS), overall survival (OS) and safety were assessed on intention-to-treat population. The association between pCR and EFS or OS was investigated in landmark population.

RESULTS

A total of 455 patients were randomised to receive lapatinib (154), trastuzumab (149) or the combination (152). Ten-year EFS estimates were 63% (95% confidence interval [CI], 54%-71%) in the lapatinib group, 64% (95% CI, 55%-72%) in the trastuzumab group and 67% (95% CI, 58%-74%) in the combination group. Ten-year OS rates were 76% (95% CI, 67%-83%), 75% (95% CI, 66%-82%) and 80% (95% CI, 73%-86%) in the lapatinib, trastuzumab and combination groups, respectively. Women who achieved a pCR had improved EFS (hazard ratio 0.48, 95% CI, 0.31-0.73) and OS (hazard ratio 0.37, 95% CI, 0.20-0.63) compared with those who did not. The numerical difference in survival according to pCR status was greater in women treated with the combination and those with hormone-receptor-negative tumours. There were no new or long-term safety concerns.

CONCLUSIONS

Patients with HER2-positive BC showed a durable survival benefit of neoadjuvant anti-HER2, irrespective of treatment arm. Patients who achieve pCR have significantly better outcomes than patients without pCR.

Impact of Anti-HER2 Therapy Alone and With Weekly Paclitaxel on the Ovarian Reserve of Young Women With HER2-Positive Breast Cancer

BACKGROUND

The potential gonadotoxicity of anti-HER2 agents remains largely unknown, and limited, conflicting evidence exists for taxanes. Antimüllerian hormone (AMH) is an established biomarker of ovarian reserve that may aid in quantifying anticancer treatment-induced gonadotoxicity.

PATIENTS AND METHODS

The present biomarker analysis of the randomized phase III neoadjuvant NeoALTTO trial included premenopausal women aged ≤45 years at diagnosis of HER2-positive early breast cancer with available frozen serum samples at baseline (ie, before anticancer treatments), at week 2 (ie, the "biological window" of anti-HER2 therapy alone), and/or at the time of surgery (ie, after completing paclitaxel + anti-HER2 therapy, before starting adjuvant chemotherapy).

RESULTS

The present analysis included 130 patients with a median age of 38 years (interquartile ratio [IQR], age 33-42 years). AMH values at the 3 time points differed significantly (P<.001). At baseline, median AMH levels were 1.29 ng/mL (IQR, 0.56-2.62 ng/mL). At week 2, a small but significant reduction in AMH levels was observed (median, 1.10 ng/mL; IQR, 0.45-2.09 ng/mL; P<.001). At surgery, a larger significant decline in AMH levels was observed (median, 0.01 ng/mL; IQR, 0.01-0.03 ng/mL; P<.001). Although the type of anti-HER2 treatment (trastuzumab and/or lapatinib) did not seem to impact the results, age and pretreatment ovarian reserve had a major influence on treatment-induced gonadotoxicity risk.

CONCLUSIONS

This NeoALTTO biomarker analysis showed that anti-HER2 therapies alone had limited gonadotoxicity but that the addition of weekly paclitaxel resulted in marked AMH decline with possible negative implications for subsequent ovarian function and fertility.

Impacts of Subtype on Clinical Feature and Outcome of Male Breast Cancer: Multicenter Study in Korea (KCSG BR16-09)

PURPOSE

The treatment of male breast cancer (MBC) has been extrapolated from female breast cancer (FBC) because of its rarity despite their different clinicopathologic characteristics. We aimed to investigate the distribution of intrinsic subtypes based on immunohistochemistry, their clinical impact, and treatment pattern in clinical practice through a multicenter study in Korea.

MATERIALS AND METHODS

We retrospectively analyzed clinical data of 248 MBC patients from 18 institutions across the country from January 1995 to July 2016.

RESULTS

The median age of MBC patients was 63 years (range, 25 to 102 years). Among 148 intrinsic subtype classified patients, 61 (41.2%), 44 (29.7%), 29 (19.5%), and 14 (9.5%) were luminal A, luminal B, human epidermal growth factor receptor 2, and triple-negative breast cancer, respectively. Luminal A subtype showed trends for superior survival compared to other subtypes. Most hormone receptor-positive patients (166 patients, 82.6%) received adjuvant endocrine treatment. Five-year completion of adjuvant endocrine treatment was associated with superior disease-free survival (DFS) in patients classified with an intrinsic subtype (hazard ratio [HR], 0.15; 95% confidence interval [CI], 0.04 to 0.49; p=0.002) and in all patients (HR, 0.16; 95% CI, 0.05 to 0.54; p=0.003).

CONCLUSION

Distribution of subtypes of MBC was similar to FBC and luminal type A was most common. Overall survival tended to be improved for luminal A subtype, although there was no statistical significance. Completion of adjuvant endocrine treatment was associated with prolonged DFS in intrinsic subtype classified patients. MBC patients tended to receive less treatment. MBC patients should receive standard treatment according to guidelines as FBC patients.

On-treatment derived neutrophil-to-lymphocyte ratio and survival with palbociclib and endocrine treatment: analysis of a multicenter retrospective cohort and the PALOMA-2/3 study with immune correlates

BACKGROUND

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have been established as a standard treatment for hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC); however, predictive biomarkers with translational relevance have not yet been elucidated.

METHODS

Data from postmenopausal women who received the CDK4/6 inhibitor palbociclib and letrozole for HR-positive, HER2-negative ABC from tertiary referral centers were analyzed (N = 221; exploratory cohort). Pre- and on-treatment neutrophil-to-lymphocyte ratio (NLR) and derived NLR (dNLR; neutrophil/[leukocyte-neutrophil]) were correlated with survival outcomes. Data from the PALOMA-2 (NCT01740427) and PALOMA-3 studies (NCT01942135) involving patients treated with endocrine treatment with or without palbociclib were also analyzed (validation cohort). Prospectively enrolled patients (N = 20) were subjected to immunophenotyping with circulating immune cells to explore the biological implications of immune cell dynamics.

RESULTS

In the exploratory cohort, palbociclib administration significantly reduced leukocyte, neutrophil, and lymphocyte counts on day 1 of cycle 2. Although the baseline dNLR was not significantly associated with progression-free survival (PFS), higher on-treatment dNLRs were associated with worse PFS (hazard ratio = 3.337, P < 0.001). In the PALOMA-2 validation cohort, higher on-treatment dNLRs were associated with inferior PFS in patients treated with palbociclib and letrozole (hazard ratio = 1.498, P = 0.009), and reduction in the dNLR after treatment was predictive of a survival benefit (hazard ratio = 1.555, P = 0.026). On-treatment dNLRs were also predictive of PFS following palbociclib and fulvestrant treatment in the PALOMA-3 validation cohort. Using flow cytometry analysis, we found that the CDK4/6 inhibitor prevented T cell exhaustion and diminished myeloid-derived suppressor cell frequency.

CONCLUSIONS

On-treatment dNLR significantly predicted PFS in patients with HR-positive, HER2-negative ABC receiving palbociclib and endocrine treatment. Additionally, we observed putative systemic immune responses elicited by palbociclib, suggesting immunologic changes upon CDK4/6 inhibitor treatment.

A Phase II Trial of S-1 and Oxaliplatin in Patients with Metastatic Breast Cancer Previously Treated with Anthracycline and Taxane (KCSG-BR07-03)

PURPOSE

This single-arm phase II trial investigate the efficacy and safety of S-1 plus oxaliplatin (SOX) in patients with metastatic breast cancer.

Materials and Methods

Patients with metastatic breast cancer previously treated with anthracyclines and taxanes were enrolled. Patients received S-1 (40-60 mg depending on patient's body surface area, twice a day, day 1-14) and oxaliplatin (130 mg/m2, day 1) in 3 weeks cycle until disease progression or unacceptable toxicity. The primary endpoint was objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumor 1.1. Secondary endpoints included time-to-progression (TTP), duration-of-response (DoR), overall survival (OS), and adverse events.

RESULTS

A total of 87 patients were enrolled from 11 institutions in Korea. Hormone receptor was positive in 54 (62.1%) patients and six (6.9%) had human epidermal growth factor receptor 2-positive disease. Forty-eight patients (85.1%) had visceral metastasis and 74 (55.2%) had more than three sites of metastases. The ORR of SOX regimen was 38.5% (95% confidence interval [CI], 26.9 to 50.0) with a median TTP of 6.0 months (95% CI, 5.1 to 6.9). Median DoR and OS were 10.3 months (95% CI, 5.5 to 15.1) and 19.4 (95% CI, not estimated) months, respectively. Grade 3 or 4 neutropenia was reported in 28 patients (32.1%) and thrombocytopenia was observed in 23 patients (26.6%).

CONCLUSION

This phase II study showed that SOX regimen is a reasonable option in metastatic breast cancer previously treated with anthracyclines and taxanes.

Abemaciclib plus fulvestrant in East Asian women with HR+, HER2- advanced breast cancer: Overall survival from MONARCH 2

MONARCH 2 is a global, randomized, double-blind, phase 3 study of abemaciclib/placebo + fulvestrant in patients with hormone receptor positive, human epidermal growth factor receptor 2-negative advanced breast cancer. The East Asian population comprised 212 (31.7%) of the 669 intent-to-treat population in the MONARCH 2 trial. Consistent with the primary analysis, this subpopulation analysis of East Asian patients indicated progression-free survival benefit in the abemaciclib arm. The median overall survival was not reached in the abemaciclib arm and was 48.9 months in the placebo arm (hazard ratio 0.80; 95% confidence interval 0.52-1.24; p = 0.377). In addition, other efficacy endpoints, including time to chemotherapy, chemotherapy free survival, and time to second disease progression, indicated benefit in the abemaciclib arm. This analysis found no new safety concerns with longer follow-up. These findings support the positive benefit-risk balance of the MONARCH 2 regimen in East Asian patients with hormone receptor positive, human epidermal growth factor receptor 2-negative advanced breast cancer.

Phase II study to investigate the efficacy of trastuzumab biosimilar (Herzuma®) plus treatment of physician's choice (TPC) in patients with heavily pretreated HER-2+ metastatic breast cancer (KCSG BR 18–14/KM10B)

We investigated the efficacy and safety of a trastuzumab biosimilar, Herzuma®, in combination with treatment of physician's choice (TPC) in patients with HER2+ metastatic breast cancer (MBC) who had failed at least two HER2 directed chemotherapies.

•

Treatment of HER2-positive breast cancer is rapidly evolving with the development of new agents. However, treatment options are still limited after progression with proven anti-HER2 therapies.

•

The combination of chemotherapy with a trastuzumab biosimilar, Herzuma®, was effective and safe in patients with heavily pre-treated HER2+ MBC.

•

Duration of response to previous anti-HER2 therapy, PIK3CA and ERBB2 mutations were associated with clinical efficacies of trastuzumab biosimilar plus chemotherapy.

Blood Test for Breast Cancer Screening through the Detection of Tumor-Associated Circulating Transcripts

Liquid biopsy has been emerging for early screening and treatment monitoring at each cancer stage. However, the current blood-based diagnostic tools in breast cancer have not been sufficient to understand patient-derived molecular features of aggressive tumors individually. Herein, we aimed to develop a blood test for the early detection of breast cancer with cost-effective and high-throughput considerations in order to combat the challenges associated with precision oncology using mRNA-based tests. We prospectively evaluated 719 blood samples from 404 breast cancer patients and 315 healthy controls, and identified 10 mRNA transcripts whose expression is increased in the blood of breast cancer patients relative to healthy controls. Modeling of the tumor-associated circulating transcripts (TACTs) is performed by means of four different machine learning techniques (artificial neural network (ANN), decision tree (DT), logistic regression (LR), and support vector machine (SVM)). The ANN model had superior sensitivity (90.2%), specificity (80.0%), and accuracy (85.7%) compared with the other three models. Relative to the value of 90.2% achieved using the TACT assay on our test set, the sensitivity values of other conventional assays (mammogram, CEA, and CA 15-3) were comparable or much lower, at 89%, 7%, and 5%, respectively. The sensitivity, specificity, and accuracy of TACTs were appreciably consistent across the different breast cancer stages, suggesting the potential of the TACTs assay as an early diagnosis and prediction of poor outcomes. Our study potentially paves the way for a simple and accurate diagnostic and prognostic tool for liquid biopsy.

Anaemia and pathologic complete response rate according to carboplatin dose in HER2+ breast cancer treated with neoadjuvant TCHP

Grade 3/4 anaemia, which is mainly induced by carboplatin, frequently occurs in patients treated with neoadjuvant docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP). However, dose reduction of carboplatin may raise concerns about the oncological outcome. This study investigated the pathologic complete response (pCR) rate, occurrence of grade 3/4 anaemia, and transfusion rate according to carboplatin dose in patients treated with neoadjuvant TCHP. We retrospectively analysed 294 patients treated with neoadjuvant TCHP between April 2015 and December 2020. Case matching was performed using propensity score matching. Among patients treated with neoadjuvant TCHP, carboplatin area under the plasma concentration-time curve 6 (AUC6) was used in 234 patients (79.6%) and upfront carboplatin AUC5 was used in 60 patients (20.4%). No significant difference in pCR rate was found between the two groups (AUC6: 70.9%, AUC5: 80.0%). In both oestrogen receptor-positive (ER+) and ER- patients, no significant differences were observed between the AUC6 and AUC5 groups (ER+: 54.3% vs. 50.0%, ER-: 81.7% vs. 86.0%). The case-matched cohort showed consistent findings. The AUC5 group had lower frequencies of grade 3/4 anaemia (18.3% vs. 34.2%) and transfusion events (10.0% vs. 21.8%) than the AUC6 group. Compared with AUC5, carboplatin at AUC6 would associate with a 2.7-fold increased risk of grade 3 or 4 chemotherapy-induced anaemia. Carboplatin AUC5 has comparable cytotoxic effects to carboplatin AUC6 in patients with HER2+ breast cancer treated with six cycles of neoadjuvant TCHP, with fewer complications associated with clinically meaningful anaemia. AUC5 may be the optimal carboplatin dose to reduce TCHP-induced anaemia in patients with HER2+ breast cancer treated with TCHP.

Trastuzumab Deruxtecan in Previously Treated HER2-Low Advanced Breast Cancer

BACKGROUND

Among breast cancers without human epidermal growth factor receptor 2 (HER2) amplification, overexpression, or both, a large proportion express low levels of HER2 that may be targetable. Currently available HER2-directed therapies have been ineffective in patients with these "HER2-low" cancers.

METHODS

We conducted a phase 3 trial involving patients with HER2-low metastatic breast cancer who had received one or two previous lines of chemotherapy. (Low expression of HER2 was defined as a score of 1+ on immunohistochemical [IHC] analysis or as an IHC score of 2+ and negative results on in situ hybridization.) Patients were randomly assigned in a 2:1 ratio to receive trastuzumab deruxtecan or the physician's choice of chemotherapy. The primary end point was progression-free survival in the hormone receptor-positive cohort. The key secondary end points were progression-free survival among all patients and overall survival in the hormone receptor-positive cohort and among all patients.

RESULTS

Of 557 patients who underwent randomization, 494 (88.7%) had hormone receptor-positive disease and 63 (11.3%) had hormone receptor-negative disease. In the hormone receptor-positive cohort, the median progression-free survival was 10.1 months in the trastuzumab deruxtecan group and 5.4 months in the physician's choice group (hazard ratio for disease progression or death, 0.51; P<0.001), and overall survival was 23.9 months and 17.5 months, respectively (hazard ratio for death, 0.64; P = 0.003). Among all patients, the median progression-free survival was 9.9 months in the trastuzumab deruxtecan group and 5.1 months in the physician's choice group (hazard ratio for disease progression or death, 0.50; P<0.001), and overall survival was 23.4 months and 16.8 months, respectively (hazard ratio for death, 0.64; P = 0.001). Adverse events of grade 3 or higher occurred in 52.6% of the patients who received trastuzumab deruxtecan and 67.4% of those who received the physician's choice of chemotherapy. Adjudicated, drug-related interstitial lung disease or pneumonitis occurred in 12.1% of the patients who received trastuzumab deruxtecan; 0.8% had grade 5 events.

CONCLUSIONS

In this trial involving patients with HER2-low metastatic breast cancer, trastuzumab deruxtecan resulted in significantly longer progression-free and overall survival than the physician's choice of chemotherapy. (Funded by Daiichi Sankyo and AstraZeneca; DESTINY-Breast04 ClinicalTrials.gov number, NCT03734029.).

Abstract 6082: TP53-GATA3 mutation status predisposes luminal-to-basal subtype conversion in advanced breast cancer patients

Background The molecular selective pressure on anti-tumor therapy drives lineage plasticity in several cancer types to develop drug resistance. The subtype conversion from luminal to triple-negative breast cancer (TNBC) subtype fuels endocrine resistance and disease aggressiveness. In this study, we analyzed mechanisms of luminal to basal subtype conversion by clinical sample sequencing and molecular study.

Method We performed whole-exome sequencing (WES) of primary and metastatic tumor tissues from breast cancer patients with luminal to basal [from HR(+)/HER2(-) to TNBC] subtype conversion (experimental, n=14) and patients with subtype maintenance (luminal to luminal subtype, control, n= 36) after adjuvant endocrine therapy. For RNA-sequencing, the subset of patients (experimental, n=14; control n=7) was further analyzed. The differences in genetic alterations and gene expression were compared between two patient groups to identify genetic predictors of subtype conversion. We also manipulated genetic factors related to subtype conversion in MCF7 cells to identify molecular signaling to drive lineage change.

Results In WES analysis, TP53 mutation was more frequently observed in luminal breast cancer patients with subtype conversion to TNBC [60% (12 out of 20 tissues in experimental group) versus 20% (8/40 tissues in control group)]. Whereas, GATA3 mutations were only observed in patients of subtype maintenance (0% versus 20%), and the mRNA level of GATA3 was downregulated after luminal-to-basal conversion. The TP53 and GATA3 mutations were both observed in the matched primary and metastatic tissues, suggesting that these mutations predisposed subtype conversion but were not acquired during the adjuvant endocrine therapy. In expression signature analysis, the patients with subtype conversion showed the upregulation of KRAS signaling and the suppression of GATA3 signature in metastatic TNBC tumors compared to primary luminal tumors. In primary tumors, RELA and MYC signatures were only upregulated in tumors that underwent subtype conversion later. We found ESR1 expression was decreased by knockdown of TP53 and GATA3 in MCF7 cells. The knockdown of TP53 and GATA3 also induced basal marker expressions, cytokeratin 5 and 14, in MCF7 cells. ESR1 expression and luminal markers were also decreased by GATA3 suppression in T47D harboring TP53 mutation.

Conclusion In luminal-type breast cancer, the subtype conversion is the one of the major obstacles for their treatment and preventing recurrence. We found the genetic alterations of TP53 mutation was the key predisposing factor of luminal to basal subtype conversion, whereas GATA3 mutation is a protecting factor for subtype conversion in luminal breast cancers. Thus, targeting TP53-GATA3 axis would be a potential therapeutic strategy to overcome endocrine resistance and block the subtype conversion in luminal type breast cancer.

Citation Format: Won-Ji Ryu, Hyun-Yi Kim, Tae Yeong Kim, Yeona Choi, Hyun Ju Hahn, Seul-Gi Kim, Gun Min Kim, Ja Seung Koo, Seung Il Kim, Joohyuk Sohn, Min Hwan Kim. TP53-GATA3 mutation status predisposes luminal-to-basal subtype conversion in advanced breast cancer patients [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 6082.

Trastuzumab deruxtecan (T-DXd) versus treatment of physician’s choice (TPC) in patients (pts) with HER2-low unresectable and/or metastatic breast cancer (mBC): Results of DESTINY-Breast04, a randomized, phase 3 study

LBA3

Background: About 55% of mBC typically categorized as HER2 negative, express low levels of HER2 (IHC 1+ or IHC 2+/ISH− by ASCO/CAP 2018 guidelines) with poor outcomes in later lines (Tarantino 2020). T-DXd has shown promising efficacy in HER2-low mBC in a phase 1 study (NCT02564900; Modi 2020). This is the primary report from DESTINY-Breast04 (NCT03734029), the first randomized, multicenter, open-label, phase 3 study comparing efficacy and safety of T-DXd vs TPC in pts with HER2-low mBC treated with 1-2 prior lines of chemotherapy in the metastatic setting. Methods: 557 pts with centrally confirmed HER2-low mBC were randomly assigned 2:1 to T-DXd 5.4 mg/kg or TPC (capecitabine, eribulin, gemcitabine, paclitaxel, or nab-paclitaxel). The primary endpoint was progression-free survival (PFS) determined by blinded independent central review (BICR) in pts with hormone receptor–positive (HR+) mBC. Key secondary endpoints (hierarchically tested after the primary endpoint) include PFS by BICR in the full analysis set (FAS; HR+/−) and overall survival (OS) in pts with HR+ mBC and in FAS. Other endpoints were objective response rate, duration of response, safety, and an exploratory analysis of pts with HR− mBC. Results: As of Jan 11, 2022, 373 and 184 pts (88.7% and 88.6% HR+ mBC) were assigned to T-DXd and TPC, respectively. Median follow-up was 18.4 months (mo; 95% CI, 17.9-19.1). Median treatment duration was 8.2 mo (range, 0.2-33.3) with T-DXd and 3.5 mo (range, 0.3-17.6) with TPC. Efficacy results are in the Table. 52.6% of pts with T-DXd vs. 67.4% of pts with TPC had grade (G) ≥ 3 treatment-emergent adverse events (TEAEs). With T-DXd, 45 pts (12.1%; 10.0% G1/2, 1.3% G3/4, 0.8% G5) had independently adjudicated drug-related interstitial lung disease [ILD]/pneumonitis vs. 1 pt (0.6% G1) with TPC. Conclusions: DESTINY-Breast04 is the first phase 3 trial of a HER2-directed therapy in pts with HER2-low mBC to show a statistically significant and clinically meaningful benefit in PFS and OS compared to standard-of-care treatment, regardless of HR status, with a generally manageable safety profile. Funding: Daiichi Sankyo, Inc., and AstraZeneca. Clinical trial information: NCT03734029. [Table: see text]

Dose-finding and -expansion studies of trastuzumab deruxtecan in combination with other anti-cancer agents in patients (pts) with advanced/metastatic HER2+ (DESTINY-Breast07 [DB-07]) and HER2-low (DESTINY-Breast08 [DB-08]) breast cancer (BC)

3025

Background: Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate composed of a humanized anti-HER2 monoclonal antibody and a topoisomerase I inhibitor payload, is approved for pts with unresectable or metastatic HER2+ BC with ≥2 prior anti-HER2–based therapies. T-DXd showed improved progression-free survival vs trastuzumab emtansine (T-DM1) as an earlier-line treatment (tx) for pts with HER2+ metastatic BC in the phase 3 DESTINY-Breast03 trial (Cortes J, et al. Ann Oncol. 2021;32:S1283-S1346. Abstract LBA1). Preliminary antitumor activity of T-DXd was shown in heavily pretreated pts with HER2-low advanced/metastatic BC in the phase 1 DS8201-A-J101 trial (Modi S, et al. J Clin Oncol. 2020;38:1887-1896). We report preliminary results from the dose-finding phase of 2 trials investigating T-DXd combination tx in HER2+ or HER2-low metastatic BC. Methods: DB-07 (phase 1b/2; NCT04538742) and DB-08 (phase 1b; NCT04556773) are 2-part, modular, open-label, multicenter trials of T-DXd combined with other anticancer tx in pts with advanced/metastatic BC that is HER2+ (DB-07) or HER2 low (DB-08). Part 1 of each study is an ongoing dose-finding phase; pts must have ≥1 prior tx for metastatic BC. Part 2 of each study is a dose-expansion phase; pts must have no (DB-07) or ≤1 (DB-08) prior tx for metastatic BC. We report preliminary results from the T-DXd + pertuzumab module of DB-07 part 1 (data cutoff: Oct 15, 2021) and T-DXd + anastrozole and T-DXd + fulvestrant modules of DB-08 part 1 (data cutoff: Sep 27, 2021); pts in the DB-08 modules must be hormone receptor positive. The part 1 primary objective was to assess safety and tolerability and determine the recommended phase 2 dose (RP2D) according to the modified toxicity probability interval-2 algorithm. Pts were followed up beyond the 21-day dose-limiting toxicity (DLT) period (28 days for T-DXd + fulvestrant) for safety events. Results: In DB-07, 7 pts were enrolled and received T-DXd 5.4 mg/kg + pertuzumab 420 mg (loading dose: 840 mg) every 3 wk (q3w; not evaluable for DLTs, n = 1). In DB-08, 6 pts were enrolled and received T-DXd 5.4 mg/kg q3w + anastrozole 1 mg daily (not evaluable for DLTs, n = 1); another 6 pts were enrolled and received T-DXd 5.4 mg/kg q3w + fulvestrant 500 mg every 4 wk (loading dose: 500 mg cycle 1 days 1 and 15). For all 3 modules, no DLTs were reported in any DLT-evaluable pts; the dose levels used in part 1 were approved to be the RP2Ds for use in the dose-expansion part of each corresponding module. No deaths on study or cases of interstitial lung disease/pneumonitis were reported to date. Conclusions: The RP2Ds for the T-DXd combinations were the standard doses for BC of each individual drug. These studies are ongoing, with additional T-DXd combinations being evaluated and further follow-up underway. Clinical trial information: NCT04538742; NCT04556773.

Subgroup analysis of patients with no prior chemotherapy in EMERALD: A phase 3 trial evaluating elacestrant, an oral selective estrogen receptor degrader (SERD), versus investigator’s choice of endocrine monotherapy for ER+/HER2-advanced/metastatic breast cancer (mBC)

1100

Background: EMERALD demonstrated significantly prolonged progression-free survival (PFS) and a manageable toxicity profile for elacestrant vs standard of care endocrine therapy (SOC) in patients with ER+/HER2- mBC following progression on prior endocrine and CDK4/6 inhibitor therapy. Benefit was observed in the overall study population and in patients with ESR1 mutations (mESR1). Here, we report a subgroup analysis from EMERALD in patients with no prior chemotherapy. Methods: EMERALD (NCT03778931) is a randomized, open-label, phase 3 trial that enrolled patients with ER+/HER2− mBC who had 1–2 lines of endocrine therapy, mandatory pretreatment with a CDK4/6 inhibitor, and ≤1 chemotherapy. Patients were randomized 1:1 to elacestrant (400 mg orally daily) or SOC (investigator’s choice of fulvestrant or aromatase inhibitor). Primary endpoints were PFS in all patients and patients with mESR1. In this analysis, we compared PFS between elacestrant and SOC in patients without prior chemotherapy. Results: Among the 477 patients enrolled in the trial, 77.8% (n = 371) had not received prior chemotherapy for mBC (median age = 64). Among patients without prior chemotherapy, treatment with elacestrant was associated with significantly prolonged PFS compared to SOC in both the overall population (hazard ratio [HR] = 0.68 [95% CI, 0.52-0.89] P = 0.004; median PFS 3.7 vs 2.0; 6-mo PFS 38% vs 23%; 12-mo PFS 27% vs 12%), and patients with mESR1 (HR = 0.54 [95% CI, 0.36-0.80] P = 0.002; median PFS 5.3 vs 1.9; 6-mo PFS 44% vs 24%; 12-mo PFS 31% vs 12%). Key treatment-related adverse events (AEs) in the no prior chemotherapy elacestrant group were nausea (25.9%), fatigue (12.7%), and hot flush (11.1%). There were no treatment-related deaths in either group. Conclusions: Among patients with ER+/HER2− mBC without prior chemotherapy, elacestrant significantly prolonged PFS compared to SOC endocrine therapy and showed favorable outcomes in this subgroup. Clinical trial information: NCT03778931.

A phase IB/II study of nivolumab in combination with eribulin in HER2-negative metastatic breast cancer (KCSG BR18-16)

1098

Background: Combining immune checkpoint inhibitors with chemotherapy has become a promising therapeutic strategy in metastatic breast cancer. Eribulin is a potent microtubule inhibitor and modulates the immune microenvironment of tumor cells. Therefore, combining eribulin to nivolumab may synergize antitumor efficacy in metastatic breast cancer. Methods: Adult patients with histologically confirmed recurrent/metastatic HER2- breast cancer were enrolled prospectively from 10 academic hospitals in Korea (ClinicalTrials.gov Identifier: NCT04061863). Key eligibility criteria included prior treatment with taxanes and/or anthracyclines, ≥1 measurable disease, and ≤2 prior cytotoxic chemotherapies in the metastatic setting. Patients received nivolumab 200 mg intravenously (IV) on day 1 plus eribulin 1.4 mg/m2 IV on day 1 and 8 of every 3 weeks until disease progression or intolerable toxicity. The dose level was determined from safety profile of three patients in run-in phase. The primary endpoint was investigator-assessed progression-free survival (PFS) rate at 6 months. Secondary endpoints included investigator-assessed objective response rate (ORR) per RECIST v1.1, disease control rate (DCR), overall survival (OS), and toxicity profile of the combination treatment. The association between PD-L1 expression by SP142 Ab and efficacy was analyzed. Results: From August 2019 to June 2021, 90 patients (HR+HER2- 45 pts/TNBC 45 pts), with a median age of 51 (range 31–71), were enrolled in the study. With a median study follow-up time of 16.3 months, 68 (75.6%) patients experienced progressive disease. PFS rate at 6-months was 49.6% and 24.1% in patients with HR+HER2- and TNBC group, respectively. Median PFS was 5.6 months (95% CI: 4.3-6.8) and 3.0 months (95% CI: 1.3-4.7) for HR+HER2- and TNBC group, respectively. ORRs were 53.3% (CR:0, PR: 24) for HR+HER2- and 21.8% (CR1, PR: 12) for TNBC. Patients with PD-L1+ tumors (PD-L1 expression ≥ 1% on TC or IC) had similar ORR compared to PD-L1- tumors (ORR 50% vs. 53.8% in HR+HER2-, 30.8% vs. 29.0% in TNBC). The most common grade 3/4 adverse event was neutropenia (15/90, 16.7%), and the most common immune-related adverse events were grade 1/2 hypothyroidism (19/90, 21.1%) and grade 1/2 pruritus (16/90, 17.8%). Five patients had discontinued study treatment due to immune-related adverse events (3 pneumonitis, 1 hepatitis, 1 skin rash). Conclusions: In this parallel phase II clinical trial, the addition of nivolumab to eribulin showed promising efficacy and tolerable safety profile in previously treated HER2- MBC. Further survival and exploratory analyses to find predictive markers will be followed. Clinical trial information: NCT04061863. [Table: see text]

Alpelisib (ALP) + fulvestrant (FUL) in patients (pts) with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer (ABC): Biomarker (BM) analyses by next-generation sequencing (NGS) from the SOLAR-1 study

1006

Background: PIK3CA mutations (mut; ~40% of HR+, HER2– ABC) are linked to poor prognosis. In SOLAR-1, ALP (PI3Kα-selective inhibitor and degrader) + FUL improved progression-free survival (PFS) vs placebo (PBO) + FUL in pts with PIK3CA-mutated HR+, HER2– ABC. Here, we focus on efficacy data by gene alterations in SOLAR-1 PIK3CA-altered (alt) cohort. Methods: SOLAR-1 was a phase 3, randomized, double-blind study of ALP (or PBO) + FUL in HR+, HER2– ABC progressing on/after an aromatase inhibitor. Baseline tissue samples with enough quantity/quality (N = 398) were retrospectively tested by NGS (FoundationOne CDx 324-gene panel) and pts grouped by PIK3CA-alteration status. Clinical benefit was assessed using PFS and hazard ratio (HR) based on tumor mutational burden (TMB) and gene alteration status in the PIK3CA-alt cohort. No multiplicity adjustment was made. Results: PIK3CA-alt (ALP, n = 120; PBO, n = 117) and PI3KCA-non-alt (ALP, n = 81; PBO, n = 80) cohorts had differential gene alteration landscapes. In the PIK3CA-alt cohort, ALP + FUL clinical benefit was seen across TMB quartiles (Q1: 0 -<2.52, Q2: 2.52 -<3.78, Q3: 3.78 -<5.04, Q4: ≥ 5.04 mut/megabase). ALP + FUL had greater benefit in pts with alt vs non-alt FGFR1/ 2 (Table). ALP + FUL benefit was independent of alterations in TP53, ESR1, CCND1, MAP3K1, and ARID1A and limited in MYC- and RAD21-alt cohorts . ALP + FUL benefit was seen in pts with alt genes in the MAPK (HR [95% CI] vs PBO: alt 0.43 [0.23 - 0.80]; non-alt 0.56 [0.40 - 0.79]) and PI3K (in addition to PIK3CA; alt 0.68 [0.38 - 1.23]; non-alt 0.48 [0.34 - 0.68]) pathways, and implicated in CDK4/6i resistance (alt 0.52 [0.30 - 0.89]; non-alt 0.53 [0.37 - 0.76]). Conclusions: The unique mut profile of PIK3CA-alt tumors did not affect ALP + FUL benefit in pts with HR+, HER2– ABC. Clinical benefit was maintained regardless of alterations in most BMs, including ESR1 and genes implicated in CDK4/6i resistance, consistent with ALP targeting the PIK3CA driver oncogene. Clinical trial information: NCT#02437318; EUDRA CT#2015-000340-42. [Table: see text]

Phase 1b/2 study of GX-I7 plus pembrolizumab in patients with refractory or recurrent (R/R) metastatic triple-negative breast cancer (mTNBC): The KEYNOTE-899 Study

1081

Background: GX-I7 (efineptakin alfa) is a hybrid Fc-fused long-acting recombinant human IL-7 which plays an essential role in the development and homeostasis of T-cells. GX-I7 can potentially enhance the anti-tumor effect of pembrolizumab via induction of T-cell activity. Here, we report results of phase 1b/2 study of GX-I7 plus pembrolizumab in patients with R/R mTNBC. Methods: Eligible patients had R/R mTNBC that failed up to 3rd lines of chemotherapy in the metastatic setting. Phase 1b patients received GX-I7 in 5 dose levels ranging from 360 µg/kg to 1,440 µg/kg every 9 (Q9W) or 12 (Q12W) weeks plus pembrolizumab 200 mg Q3W (n=51). Phase 2 is an expansion cohort where 33 patients were treated with the recommended phase 2 dose (RP2D). The primary objective was to determine the RP2D for phase 1b and to assess the objective response rate (ORR) for phase 2. Results: The study included 84 patients (phase 1b, n=51; phase 2, n=33) and 53.6% (45/84) of patients have received 2nd to 3rd lines of previous therapy. In phase 1b, one dose-limiting toxicity (DLT; grade 3 skin rash) was reported in the 1,440 µg/kg cohort and GX-I7 1,200 µg/kg Q9W was selected as RP2D. The ORRs were 15.7% [95% confidence interval (CI): 7.0 – 28.6] for phase 1b (n=51) and 21.2% [95% CI: 9.0 – 38.9] for phase 2 (n=33). Median PFS was 2.4 months (95% CI: 2.1 – 2.7) at the median follow-up of 10.4 months for all patients combined (n=84). GX-I7 induced up to 3.6-fold (range 1.2 – 8.1) increase in absolute lymphocyte counts (including CD4+ and CD8+ T cell) in all dose levels. The most common treatment-related adverse events (AEs) of any grade were injection site reaction (50.0%), ALT increased (39.3%), pyrexia (38.1%) and rash (35.7%). The additional correlative study data will be presented. Conclusions: GX-I7 in combination with pembrolizumab demonstrated a manageable safety profile with promising anti-tumor activity in patients with R/R metastatic TNBC. Clinical trial information: NCT03752723. [Table: see text]

Impact of anti-HER2 therapy alone and in association with weekly paclitaxel on the ovarian reserve of young women with HER2-positive early breast cancer: Biomarker analysis of the NeoALTTO trial

12084

Background: The potential gonadotoxicity of anti-HER2 agents remains largely unknown and limited conflicting evidence exists for taxanes. Anti-Mullerian hormone (AMH) is an established biomarker of ovarian reserve; its measurement during systemic therapies may aid in indicating gonadotoxicity, in the diagnosis and prediction of primary ovarian insufficiency (POI). The present analysis explored for the first time the impact of anti-HER2 therapy alone and then combined with weekly paclitaxel on ovarian reserve measured by AMH levels in breast cancer (BC) patients not previously exposed to anthracycline and cyclophosphamide. Methods: This biomarker analysis of the NeoALTTO (NCT00553358) randomized phase III neoadjuvant trial included premenopausal women aged ≤45 years at diagnosis of HER2-positive early BC with available frozen serum samples at baseline (i.e. before administering any anticancer treatment), at week 2 (i.e. “biological window” of anti-HER2 therapy alone) and/or at the time of surgery (i.e. after completion of paclitaxel plus anti-HER2 therapy and before starting adjuvant chemotherapy). Central AMH testing was performed with the Roche Elecsysâ AMH Plus assay (LoD = 0.01 ng/ml). AMH levels during anti-HER2 therapy alone and then combined with paclitaxel were assessed as a measure of treatment acute gonadotoxicity. The impact of different anti-HER2 agents, patients’ age, and baseline AMH levels on treatment gonadotoxicity were also investigated. Results: The present analysis included 130 patients with a median age of 38 years (IQR: 33-42 years). AMH values at the 3 time points differed significantly from each other (p < 0.001). At baseline, median AMH levels were 1.29 ng/mL (IQR 0.56 – 2.62 ng/mL). At week 2, a small but significant reduction in AMH levels was observed (median value: 1.10 ng/mL, IQR 0.45 – 2.09 ng/mL, p < 0.001). At surgery, there was a larger significant decline in AMH levels (median value: 0.01 ng/mL, IQR 0.01 – 0.03 ng/mL, p < 0.001). There was no significant difference between treatment arms (trastuzumab vs. lapatinib vs. trastuzumab plus lapatinib) in the degree of reduction in AMH levels at week 2 (p = 0.763) and at surgery (p = 0.700). Age and pre-treatment ovarian reserve had a major influence on treatment-induced gonadotoxicity risk, with older age and lower AMH levels at diagnosis being associated with a greater negative impact. Conclusions: This biomarker analysis of the NeoALTTO trial showed for the first time that anti-HER2 therapies alone had limited gonadotoxicity but the addition of weekly paclitaxel resulted in marked AMH decline which likely has implications for subsequent ovarian function and fertility. These data highlight the importance of oncofertility counselling among all premenopausal women with HER2-positive BC receiving systemic anticancer treatments. Clinical trial information: NCT00553358.

Retrospective study to estimate the prevalence of HER2-low breast cancer (BC) and describe its clinicopathological characteristics

1087

Background: Approximately 50% of BCs traditionally categorized as HER2 negative (HER2-neg) express low levels of HER2 (IHC 1+ or IHC 2+/ISH-; Miglietta, NPJ Breast Cancer 2021). HER2-targeted therapies for HER2-low metastatic BC (mBC) are under investigation (eg, T-DXd in the phase 3 DESTINY-Breast04 study; NCT03734029), but HER2 assays currently used to select patients (pts) for approved anti-HER2 therapies are optimized for high HER2 expression and are not validated for HER2-low detection. A recent study found relatively poor agreement (<70% interrater agreement) in evaluation of IHC scores of 0 and 1+ using current HER2 assays (Fernandez, JAMA Oncol 2022). Our objectives were to assess the prevalence of HER2-low among HER2-neg based on rescored HER2 IHC slides after training on low-end expression scoring and to describe pt characteristics of HER2-low vs HER2 IHC 0 mBC. Preliminary results are reported for 233 of 1000 planned pts. Methods: This multicenter, retrospective study (NCT04807595) included pts with confirmed HER2-neg unresectable/mBC diagnosed between 2015 and 2017. Local laboratories, blinded to historical HER2 scores, rescored HER2 IHC-stained slides. HER2 was assessed using Ventana 4B5 and other assays. BCs were categorized as HER2-low or HER2 IHC 0. The prevalence of HER2-low BC among pts originally scored as HER2-neg was measured. Demographics (eg, age, country, race) and clinicopathological characteristics were examined via medical charts/electronic health records. Concordance between historical HER2 scores and rescores was assessed. Results: HER2 rescores were obtained for 233 pts (mean age, 54 y). HER2-low prevalence was 63.2% overall and numerically greater in hormone receptor (HR)–positive vs HR-negative subgroups (66.1% vs 54.8%; Table). No notable differences in prevalence were seen among different HER2 assays or in demographic/baseline disease characteristics between the HER2-low and HER2 IHC 0 groups. Concordance rate between historical and rescored slides for HER2-status classification was 82.3%. The presentation will include an expanded data set (≈400 pts) with additional results. Conclusions: Data on HER2-low prevalence in BC is limited. Preliminary data from this study of mBC samples suggest a somewhat higher prevalence estimate (≈63%) than a previous study of primary BC samples (≈50%). Concordance was 82%; ongoing analyses with updated data will clarify the concordance between rescored and historical HER2 slides. These data can support development of best practices for identifying pts with HER2-low expression who may benefit from HER2-targeted therapies. Clinical trial information: NCT04807595. [Table: see text]

KEYNOTE-B49: A phase 3, randomized, double-blind, placebo-controlled study of pembrolizumab plus chemotherapy in patients with HR+/HER2- locally recurrent inoperable or metastatic breast cancer

TPS1118

Background: HR+/HER2− advanced breast cancer that progresses on endocrine therapy is treated with chemotherapy (chemo). The phase 1b KEYNOTE-028 trial showed durable activity with pembrolizumab (pembro) monotherapy in previously treated HR+/HER2−, PD-L1–positive (combined positive score [CPS] ≥1) advanced breast cancer. KEYNOTE-B49 (NCT04895358) is a phase 3, randomized, double-blind study of pembro + chemo vs placebo (pbo) + chemo in centrally assessed PD-L1–positive, HR+/HER2− locally recurrent inoperable or metastatic breast cancer (mBC) after progression on prior endocrine therapy. Methods: ∼800 patients (pts) with HR+/HER2− locally recurrent inoperable or mBC who are candidates for chemo (no prior chemo for metastatic disease) with PD-L1 CPS ≥1 and documented progression on prior endocrine therapy will be enrolled. Prior endocrine therapy comprises ≥2 lines (≥1 in combination with a CDK4/6 inhibitor) in the metastatic setting or 1 line with CDK4/6 inhibitor treatment for mBC in pts who had a relapse within 24 mo of primary surgery. Pts without prior CDK4/6 inhibitor treatment may enroll if they had progressed within 6 mo of starting endocrine therapy for metastatic disease and had previously relapsed within 24 mo of primary tumor surgery while on adjuvant endocrine therapy. Pts are randomized 1:1 to receive pembro 200 mg IV or pbo Q3W, each in combination with investigator’s choice of chemo: paclitaxel 90 mg/m2 IV on days 1, 8, and 15 Q4W; nab-paclitaxel 100 mg/m2 IV on days 1, 8, and 15 Q4W; liposomal doxorubicin 50 mg/m2 IV on day 1 Q4W; or capecitabine 1000 mg/m2 PO BID on days 1–14 Q3W. Randomization is stratified by tumor PD-L1 (CPS 1–9 vs ≥10), presence of visceral metastases (yes vs no), and chemo on-study (taxanes vs liposomal doxorubicin vs capecitabine). Treatment is continued until disease progression, unacceptable toxicity, withdrawal, or, for pembro/pbo, completion of 35 cycles (̃2 years); chemo can be continued per investigator discretion. Tumor PD-L1 status is determined centrally using the PD-L1 IHC 22C3 pharmDx assay (Agilent Technologies; Carpinteria, CA, USA). Radiologic assessments are performed Q9W for 54 wk and then Q12W thereafter. AEs occurring from randomization until 30 d after treatment discontinuation (90 d for serious AEs) are graded per NCI-CTCAE v 5.0. Primary endpoints are PFS per RECIST v1.1 by BICR and OS in pts with PD-L1 CPS ≥10 and ≥1 tumors, separately. Enrollment is ongoing at 204 international sites. Clinical trial information: NCT04895358.

Impact of ribociclib (RIB) dose modifications (mod) on overall survival (OS) in patients (pts) with HR+/HER2- advanced breast cancer (ABC) in MONALEESA(ML)-2

1017

Background: The phase 3 ML-2, -3, and -7 trials all demonstrated consistent and statistically significant OS benefit with RIB (starting dose: 600 mg/d 3 wk on/1 wk off) vs PBO in pts with HR+/HER2− ABC. RIB dose mod (reductions and/or interruptions) when needed did not impact OS benefit with RIB + endocrine therapy (ET) in previous analyses of ML-3/-7. Here we present data on the effect of RIB dose mod on OS in postmenopausal pts with HR+/HER2− ABC in ML-2. Methods: ML-2 (NCT01958021) enrolled postmenopausal pts randomized 1:1 to first-line RIB + letrozole (LET) or PBO + LET. Landmark (LM) analyses of OS were performed to evaluate the association between dose reductions (yes vs no) and OS. Multiple LM times were considered to determine the sensitivity of the findings. As an alternative to LM analysis, a Cox proportional hazards model with a time-varying covariate was performed. Two time-dependent variables, dose reduction (with/without mod from 600 mg starting dose) and relative dose intensity 2 (RDI2), were included in the respective model as covariates to explore the association with OS. To account for differences in time to first dose mod, RDI2 reflects the post–dose mod period. Median (m) OS was obtained using a modified Kaplan-Meier method. Results: At data cutoff (June 10, 2021; m follow-up, 49.35 [range, 0-86.7] mo), 209 of 334 pts (62.6%) had ≥ 1 RIB dose reduction and 125 of 334 (37.4%) had 0 RIB dose reduction. LM analyses by dose reduction are presented (Table). mOS was 66.0 (95% CI, 57.6-75.7) mo in pts with ≥ 1 RIB dose reduction vs 60.6 (95% CI, 42.5-79.2) mo in pts with no RIB dose reductions (HR, 0.87 [95% CI, 0.65-1.18]). RDI2 was classified according to tertile: low (< 64.27%), medium (64.27%-95.86%), and high (> 95.86%). In pts with low, medium, and high RDI2, mOS was 62.6 (95% CI, 50.0-80.7) mo, 63.9 (95% CI, 48.8-not reached [NR]) mo, and 65.3 (95% CI, 50.5-NR) mo, respectively (HR low vs high, 0.99 [95% CI, 0.69-1.42]; HR medium vs high, 0.97 [95% CI, 0.62-1.38]). Conclusions: In this exploratory analysis of ML-2, OS benefit was maintained in pts with HR+/HER2− ABC who required mod from the recommended starting dose of RIB (600 mg/d 3 wk on/1 wk off). No relationship was observed between OS and RIB dose reduction or RDI2; OS benefit with RIB was observed in all groups. Clinical trial information: NCT01958021. [Table: see text]

Impacts of subtypes on clinical feature and outcome of male breast cancer

e12528

Background: The treatment of male breast cancer (MBC) has been extrapolated from female breast cancer (FBC) because of its rarity despite their different clinicopathologic characteristics. We aimed to investigate the distribution of intrinsic subtypes based on immunohistochemistry (IHC), their clinical impact, and treatment pattern in clinical practice through a multicenter study in Korea. Methods: We retrospectively analyzed clinical data of 248 MBC patients 18 institutions across the country from January 1995 to July 2016. Results: The median age of MBC patients was 63 years (range: 25–102 years). Among the 148 patients that underwent intrinsic subtype classification, 61 (41.2%), 44 (29.7%), 29 (19.5%), and 14 (9.5%) were luminal A, luminal B, HER2, and triple-negative breast cancer (TNBC), respectively. TNBC patients showed inferior survival compared with those with other subtypes. Of the 221 patients with operable breast cancer, 108 (48.6%) received adjuvant chemotherapy and 52 (23.5%) received adjuvant radiation therapy. Most hormone receptor-positive patients (166 patients, 82.6%) received adjuvant endocrine treatment. Five-year completion of adjuvant endocrine treatment was associated with superior disease-free survival (DFS) in patients classified with an intrinsic subtype (hazard ratio [HR] = 0.19, 95% confidence interval [CI] 0.005–0.65, P = 0.008) and in all patients (HR = 0.16, 95% CI 0.05–0.54, P = 0.003). Conclusions: Distribution of subtypes of MBC was similar to FBC and luminal type A was most common. Overall survival tended to be improved for luminal A subtype although there was no statistical significance. Completion of adjuvant endocrine treatment was associated with prolonged DFS in intrinsic subtype classified patients. MBC patients have tended to receive les treatment. MBC patients should be treated with standard guideline as FBC patients receive.

Phase 3 study of tucatinib or placebo in combination with trastuzumab and pertuzumab as maintenance therapy for HER2+ metastatic breast cancer (HER2CLIMB-05, trial in progress)

TPS1108

Background: The current first-line (1L) standard of care (SOC) for human epidermal growth factor receptor 2-positive (HER2+) metastatic breast cancer (MBC) is trastuzumab (T) plus pertuzumab (P) and a taxane. Despite advances in 1L SOC, most patients (pts) progress during maintenance therapy with T+P. Tucatinib is a tyrosine kinase inhibitor (TKI) approved in combination with T and capecitabine for adults with HER2+ MBC, with and without brain metastases (BM). In HER2CLIMB, the addition of tucatinib significantly prolonged progression-free survival (PFS) and overall survival (OS) in pts with HER2+ MBC and was well tolerated. Adding tucatinib also reduced the risk of disease progression or death in pts with untreated and/or active BM (Murthy et al. 2020, Curigliano et al. 2021). HER2CLIMB-05 investigates whether adding tucatinib to 1L SOC as maintenance therapy will extend PFS while maintaining quality of life (QOL). Methods: HER2CLIMB-05 (NCT05132582) is a phase 3, randomized, double-blind study evaluating tucatinib plus T+P as maintenance therapy for HER2+ MBC. Approximately 650 pts will be enrolled. Eligible pts will have advanced HER2+ disease, no progression on 4–8 cycles of prior 1L SOC, ECOG Performance Status of 0 or 1, and no or asymptomatic BM. Exclusion criteria include prior treatment with anti-HER2 and/or anti-epidermal growth factor receptor TKI (prior SOC for early BC is permitted) or inability to undergo contrast magnetic resonance imaging of the brain. Pts will be randomized 1:1 to receive either tucatinib or placebo twice daily, with T+P once every 21 days. Pts with HR+ disease may receive endocrine therapy. The primary endpoint is investigator-assessed PFS. Secondary endpoints include OS (key endpoint), time to deterioration of health-related QOL, central nervous system PFS, safety, and pharmacokinetic (PK) parameters. PFS and OS will be compared using a 2-sided stratified log-rank test between treatment groups. Time-to-event endpoints will be summarized using the Kaplan–Meier method. PK and safety data will be summarized using descriptive statistics. Enrollment is ongoing in the US, with additional sites planned. Clinical trial information: NCT05132582.

Copy number aberration burden on circulating tumor DNA predicts recurrence risk after neoadjuvant chemotherapy in patients with triple-negative breast cancer: Post-hoc analysis of phase III PEARLY trial

603

Background: Our previous study reported prognostic significance of copy number aberration (CNA) burden on low-pass whole genome sequencing (LP-WGS) based circulating tumor DNA (ctDNA) analysis in metastatic breast cancer patients. Here, we report the prognostic value of ctDNA CNA burden measured before neoadjuvant chemotherapy in stage II-III triple-negative breast cancer (TNBC) patients enrolled in phase III PEARLY trial (NCT02441933, BIG Supporter Study BIG 19-01, KCSG BR15-01). Methods: The PEARLY trial was performed as a randomized, open-label, multicenter, phase III study to test the efficacy and safety of adding carboplatin to (neo)adjuvant chemotherapy in patients with stage II-III TNBC. Patients were randomized in a 1:1 ratio to receive 4 cycles of AC followed by the taxane or taxane plus carboplatin (AUC 5, tri-weekly 4 cycles) as neoadjuvant or adjuvant therapy. This post-hoc baseline ctDNA analysis (before neoadjuvant chemotherapy) included only the neoadjuvant patient cohort with available baseline ctDNA results (n = 465, median follow-up 16.8 months), while it was blinded for randomization information (carboplatin or not). We used "I-score" method to estimate CNA burden of ctDNA by LP-WGS to be matched with disease-free survival (DFS) after primary surgery. Results: The baseline ctDNA I-score level was positively associated with clinical T and N stage, while baseline I-score was not different between patients with pathologic complete response (pCR) and non-pCR. We listed 465 patients in the order in which they underwent primary surgery, and then alternated patients to be assigned to exploratory cohort (n =232) and validation cohort (n = 233). The DFS was significantly shorter in high I-score (I-score ≥ 7.81) patients compared with low I-score (I-score < 7.81) patients in exploratory cohort. The high I-score independently predicted poor DFS adjusted for clinical T stage, clinical N stage, and pCR status (hazard ratio [HR] 3.88, p = 0.003). In the validation cohort, high I-score was validated to be associated poorer DFS, and multivariate Cox analysis validated the independent prognostic impact of I-score on DFS (HR 2.04 , p = 0.050). The high baseline I-score patients showed shorter DFS both in pCR-positive and pCR-negative patients. The 12-month DFS rate for pCR (+)/Low I-score patients was 98%, whereas that of pCR(-)/High I-score patients was 61.3 % in the validation cohort. Conclusions: The baseline ctDNA CNA burden on LP-WGS before neoadjuvant chemotherapy robustly predicts recurrence risk in stage II-III TNBC patients. The ctDNA I-score showed prognostic value independently from pCR status, suggesting ctDNA I-score can serve as a useful clinical determinant for escalating or de-escalating (neo)adjuvant strategy in TNBC patients. Clinical trial information: NCT02441933.

Molecular Characterization of BRCA1 c.5339T>C Missense Mutation in DNA Damage Response of Triple-Negative Breast Cancer

BRCA1 L1780P BRCT domain mutation has been recognized as a pathogenic mutation in patients with breast cancer. However, the molecular significance of this mutation has not yet been studied in triple-negative breast cancer (TNBC) cells in vitro. We established MDA-MB 231, HCC1937, and HCC1395 TNBC cell lines expressing BRCA1 L1780P mutant. BRCA1 L1780P mutant TNBC cells showed increased migration and invasion capacity, as well as increased sensitivity to olaparib and carboplatin compared to BRCA1 wild-type cells. BRCA1 L1780P mutant TNBC cells showed decreased RAD51 expression and reduced nuclear RAD51 foci formation following carboplatin and olaparib treatment. The molecular interaction between p-ATM and BRCA1 was abrogated following introduction of BRCA1 L1780P mutant plasmid in TNBC cells, suggesting that the BRCA1 L1780P mutation disrupts the p-ATM-BRCA1 protein-protein interaction. We established an olaparib-resistant BRCA1 L1780P mutant TNBC cell line by chronic drug treatment. Olaparib-resistant cell lines showed upregulation of RAD51 expression upon olaparib treatment, and reduction in RAD51 expression in olaparib-resistant cells restored olaparib sensitivity. Collectively, these results suggest that the BRCA1 L1780P mutation impairs RAD51 recruitment by disrupting p-ATM-BRCA1 interaction, which is a crucial molecular factor in homologous recombination and olaparib sensitivity. Further therapeutic targeting of RAD51 in BRCA1 L1780P mutant breast cancer is warranted.

Updated Overall Survival of Ribociclib plus Endocrine Therapy versus Endocrine Therapy Alone in Pre- and Perimenopausal Patients with HR+/HER2- Advanced Breast Cancer in MONALEESA-7: A Phase III Randomized Clinical Trial

PURPOSE

Ribociclib plus endocrine therapy (ET) demonstrated a statistically significant progression-free survival and overall survival (OS) benefit in the phase III MONALEESA-7 trial of pre-/perimenopausal patients with hormone receptor (HR)-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC). The median OS was not reached in the ribociclib arm in the protocol-specified final analysis; we hence performed an exploratory OS and additional outcomes analysis with an extended follow-up (median, 53.5 months).

PATIENTS AND METHODS

Patients were randomized to receive ET [goserelin plus nonsteroidal aromatase inhibitor (NSAI) or tamoxifen] with ribociclib or placebo. OS was evaluated with a stratified Cox proportional hazard model and summarized with Kaplan-Meier methods.

RESULTS

The intent-to-treat population included 672 patients. Median OS was 58.7 months with ribociclib versus 48.0 months with placebo [hazard ratio = 0.76; 95% confidence interval (CI), 0.61-0.96]. Kaplan-Meier estimated OS at 48 months was 60% and 50% with ribociclib and placebo, respectively. Subgroup analyses were generally consistent with the OS benefit, including patients who received NSAI and patients aged less than 40 years. Subsequent antineoplastic therapies following discontinuation were balanced between the ribociclib (77%) and placebo (78%) groups. Use of cyclin-dependent kinase 4/6 inhibitors after discontinuation was higher with placebo (26%) versus ribociclib (13%). Time to first chemotherapy was significantly delayed with ribociclib versus placebo. No drug-drug interactions were observed between ribociclib and either NSAI.

CONCLUSIONS

Ribociclib plus ET continued to show significantly longer OS than ET alone in pre-/perimenopausal patients, including patients aged less than 40 years, with HR+/HER2- ABC with 53.5 months of median follow-up (ClinicalTrials.gov, NCT02278120).

Novel Preosteoclast Populations in Obesity-Associated Periodontal Disease

Although there is a clear relationship between the degree of obesity and periodontal disease incidence, the mechanisms that underpin the links between these conditions are not completely understood. Understanding that myeloid-derived suppressor cells (MDSCs) are expanded during obesity and operate in a context-defined manner, we addressed the potential role of MDSCs to contribute toward obesity-associated periodontal disease. Flow cytometry revealed that in the spleen of mice fed a high-fat diet (HFD), expansion in monocytic MDSCs (M-MDSCs) significantly increased when compared with mice fed a low-fat diet (LFD). In the osteoclast differentiation assay, M-MDSCs isolated from the bone marrow of HFD-fed mice showed a larger number and area of osteoclasts with a greater number of nuclei. In the M-MDSCs of HFD-fed mice, several osteoclast-related genes were significantly elevated when compared with LFD-fed mice according to a focused transcriptomic platform. In experimental periodontitis, the number and percentage of M-MDSCs were greater, with a significantly larger increase in HFD-fed mice versus LFD-fed mice. In the spleen, the percentage of M-MDSCs was significantly higher in HFD-fed periodontitis-induced (PI) mice than in LFD-PI mice. Alveolar bone volume fraction was significantly reduced in experimental periodontitis and was further decreased in HFD-PI mice as compared with LFD-PI mice. The inflammation score was significantly higher in HFD-PI mice versus LFD-PI mice, with a concomitant increase in TRAP staining for osteoclast number and area in HFD-PI mice over LFD-PI mice. These data support the concept that M-MDSC expansion during obesity to become osteoclasts during periodontitis is related to increased alveolar bone destruction, providing a more detailed mechanistic appreciation of the interconnection between obesity and periodontitis.

Abstract P2-12-13: Pathologic complete response rate according to the carboplatin dose in patients with non-metastatic HER2+ breast cancer treated with neoadjuvant docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP)

Purpose In the patients treated with neoadjuvant docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP) regimen, grade 3-4 anemia occurs frequently during the treatment course. Anemia develops mainly by cytotoxic drug including carboplatin. By contrast, dose reduction of carboplatin could raise concerns about the oncologic outcome. We compared the pathologic complete response (pCR) rate and grade 3-4 anemia/transfusion rate according to the dose of carboplatin among the patients undergoing neoadjuvant TCHP. Method We retrospectively analyzed 294 patients who treated with neoadjuvant TCHP between Apr 1, 2015 and Dec 31, 2020. Clinicopathological features were collected by electronic medical record review. Hemoglobin levels were measured at baseline, before each cycle of chemotherapy, and after the chemotherapy completion. Multivariable binary logistic regression analysis was performed to identify predictive factors for grade 3-4 anemia and transfusion event. Result In a total of 294 patients, neoadjuvant TCHP with carboplatin AUC6 were initiated in 234 (79.6%, 234 of 294), whereas upfront carboplatin AUC5 were concurrently administered in 60 (20.4%, 60 of 294). There was no statistical difference in the pCR rate between the two groups (70.9% in the AUC6, 80.0% in the AUC5; p=0.159). In the both ER+ and ER-, there were no significant differences between the AUC6 and AUC5 (54.3% and 50.0% in the ER+; 81.7% and 86.0% in the ER-). Tumor and nodal stage were not different between the two groups. The AUC5 group had less grade 3-4 anemia (18.3%, 11 of 60 vs 34.2%, 80 of 234) and transfusion event (10.0%, 6 of 60 vs 21.8%, 51 of 234) compared with the AUC6 group. Multivariable analysis demonstrated that baseline hemoglobin level under 12g/dL and ≥2g/dL hemoglobin down after first chemotherapy are independent risk factors for grade3-4 anemia or blood transfusion before surgery. Conclusion The pCR rate was not different according to the initial carboplatin dose in the HER2+ breast cancer treated with neoadjuvant TCHP. We suggest that the dose of carboplatin could be optimized as AUC5 to reduce TCHP-induced anemia and transfusion rate among Asian HER2-positive breast cancer patients treated with TCHP. Baseline low hemoglobin level under 12 g/dL or rapid hemoglobin down after first cycle are risk factors for TCHP-induced anemia.

Table 1.The pathologic complete response (pCR) rate, distribution of anemia grade and transfusion rate according to AUCVariablesAUC6AUC5TotalP-valueOverall (N=294)0.159pCR166 (70.9%)48 (80.0%)214 (72.8%)Non-pCR68 (29.1%)12 (20.0%)80 (27.2%)Total234 (100.0%)60 (100.0%)294 (100.0%)ER-positive (N=102)0.793pCR50 (54.3%)5 (50.0%)55 (53.9%)Non-pCR42 (45.7%)5 (50.0%)47 (16.1%)Total92 (100.0%)10 (100.0%)102 (100.0%)ER-negative (N=192)0.487pCR116 (81.7%)43 (86.0%)159 (82.8%)Non-pCR26 (18.3%)7 (14.0%)33 (17.2%)Total142 (100.0%)50 (100.0%)192 (100.0%)Anemia grade (N=294)0.0181 or 2154 (65.8%)49 (81.7%)203 (69.0%)3 or 480 (34.2%)11 (18.3%)91 (31.0%)Transfusion (N=294)0.039No183 (78.2%)54 (90.0%)237 (80.6%)Yes51 (21.8%)6 (10.0%)57 (19.4%)

Citation Format: Jung Hwan Ji, Soong June Bae, Seul-Gi Kim, Min Hwan Kim, Gun-Min Kim, Joohyuk Sohn, Jee Hung Kim, Sung Gwe Ahn, Joon Jeong. Pathologic complete response rate according to the carboplatin dose in patients with non-metastatic HER2+ breast cancer treated with neoadjuvant docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP) [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 P2-12-13.

Abstract PD13-07: Activity and biomarker analyses from a phase Ia/b study of giredestrant (GDC-9545; G) with or without palbociclib (palbo) in patients with estrogen receptor-positive, HER2-negative locally advanced/metastatic breast cancer (ER+/HER2- LA/mBC)

Background A mainstay of ER+ BC treatment is to target ER activity and/or estrogen synthesis; however, during or after endocrine therapy (ET), many patients either relapse or develop resistance to such treatments due to several mechanisms, including ESR1 mutations which can be drivers of estrogen-independent transcription and proliferation. The majority of tumors remain dependent on ER signaling, and it is possible that patients will be responsive to second- or third-line ET after they have progressed on previous therapies. The highly potent, nonsteroidal oral selective ER antagonist and degrader G achieves robust ER occupancy and is active in patients with either ESR1-wildtype or -mutant tumors and in patients who had previously been treated with ET. G was well tolerated as a single agent and in combination with palbo, with antitumor activity shown in the nonrandomized, open-label, dose-escalation and -expansion, phase Ia/b GO39932 study (NCT03332797). We present updated activity and biomarker analyses in patients treated with 30 mg G monotherapy and those treated with 100 mg G + 125 mg palbo ± luteinizing hormone-releasing hormone (LHRH) agonists (clinical cutoff: Apr 16, 2021); 30 mg has since been selected as the dose in both the single agent and combination settings. Methods Eligible patients had ≤2 prior therapies for LA/mBC, disease recurrence, or progression while on adjuvant ET for ≥24 months and/or ET for LA/mBC, and tumor response or stable disease ≥6 months. All were postmenopausal (premenopausal women were allowed co-administered LHRH agonists with 100 mg G). Oral G was given daily on Days (D)1-28 of each 28-day cycle (C); 125 mg palbo, on a 21-day on/7-day off schedule. Modulation of ER signaling and proliferation of paired pre- and on-treatment (C2D8) tumor biopsies were assessed with immunohistochemistry for ER, progesterone receptor (PgR), and the proliferation marker Ki67, as well as with gene expression analysis of a predefined set of 38 ER target genes using the Illumina TruSeq RNA Access method. Plasma samples collected pre- and on-treatment (C1D15 and/or C2D1) were assessed for circulating tumor (ct)DNA using a digital PCR BEAMing assay detecting a total of 22 mutations across ESR1, AKT1, and PIK3CA. Results Objective response rates in patients with measurable disease at baseline were 20.0% in the 30 mg G group (6/30 patients) and 47.7% in the 100 mg G + palbo ± LHRH (combination) group (21/44). Clinical benefit rates were 55.0% (22/40 patients) and 81.3% (39/48), respectively. Overall, 21 pre- and on-treatment-paired tumor biopsies were collected in the 30 mg (n=13) and combination (n=8) groups. Consistent downregulation of ER, PgR, Ki67, and ER pathway activity was observed at C2D8, regardless of clinical benefit or baseline ESR1 mutation, demonstrating consistent on-target activity of G. Stronger Ki67, ER, and PgR suppression was seen with the addition of palbo to G. Of the 36 patients across both cohorts with a detectable ctDNA baseline ESR1 mutation, 16 had &gt;1 baseline ESR1 mutation. Of the eight unique ESR1 mutations detected, none showed an association with response. At C2D1, 34 patients had a decrease in ESR1 ctDNA levels from baseline, of which 27 became undetectable for ESR1 ctDNA. Early changes in PIK3CA and AKT1 ctDNA levels, but not ESR1, trended with response. Conclusions Encouraging clinical activity was observed with single agent G at 30 mg and with G at 100 mg in combination with palbo. Biomarker analyses demonstrated consistent biologic activity of G, and largely consistent decreases of ESR1 ctDNA levels. Further updated activity and biomarker data, including PAM50 subtype classifications, will be presented.

Citation Format: Nicolas C Turner, Sherene Loi, Heather M Moore, Ching-Wei Chang, Jennifer Eng-Wong, Aditya Bardia, Valentina Boni, Joohyuk Sohn, Komal L Jhaveri, Elgene Lim. Activity and biomarker analyses from a phase Ia/b study of giredestrant (GDC-9545; G) with or without palbociclib (palbo) in patients with estrogen receptor-positive, HER2-negative locally advanced/metastatic breast cancer (ER+/HER2- LA/mBC) [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 PD13-07.