BRCA1-associated Breast Cancer Research Articles

Mitomycin C in the treatment of early triple-negative locally advanced BRCA-associated breast cancer

Rationale. BRCA1 associated triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer. At the same time, carcinomas that develop in carriers of BRCA1 mutations are characterized by extremely high sensitivity to DNA-damaging chemotherapy. Mitomycin C alone or in combination with platinum agents has already demonstrated promising results in the treatment of BRCA-associated ovarian cancer (OC) and metastatic breast cancer. In this article, we present the results of a retrospective study aimed at comparing standard neoadjuvant chemotherapy regimens (NACT) with mitomycin-based regimens for primary locally advanced BRCA1-associated TNBC.The aim of the study is to determine the effectiveness of the combination of mitomycin and platinum compounds during neoadjuvant therapy in patients with primary locally advanced BRCA1 – associated TNBC.Materials and methods. The study included 89 patients diagnosed with primary locally advanced BRCA1-associated TNBC. Patients were divided into three groups depending on the therapy: 1) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel (n = 48) (AC + T), 2) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel and carboplatin (n = 27) (AC + TCbP), 3) mitomycin C plus platinum followed by 12 weekly injections of paclitaxel (n = 14) (MR + T). Pathological complete response (pCR) rates were compared.Results. The pCR rate in the MP+T group was 10/14 (71%). In patients with BRCA1-associated breast cancer who received AC + T and AC + TCbP regimens as NACT, the pCR rate was 17/48 (35%) and 19/27 (70%), respectively. The difference in pCR rate between mitomycin-containing therapy and the standard AC + T regimen was statistically significant (p = 0.03); the frequency of regressions was comparable to the frequency in the AC + TCbP group. During the 20-month follow-up period, no relapses were observed in the MR + T group. Relapses were more frequent in the AC + T group compared with the AC + TCbP group (16/48 (33%) vs 1/27 (4%), p = 0.003, Fisher’s exact test). The toxicity profile of the mitomycin-containing regimen included hematologic adverse events, the most common of which were anemia and leukopenia. Compared to standard regimens, nausea was significantly less pronounced. No patients reported alopecia with this regimen.Conclusions. The addition of mitomycin C to neoadjuvant therapy for BRCA1-associated TNBC may be a promising treatment option for this category of patients and merits further study.

Abstract PO2-06-07: A Randomized Phase II Comparison of Single-Agent Carboplatin versus the Combination of Carboplatin and Everolimus for the Treatment of Advanced Triple Negative Breast Cancer

Abstract Background: Both TNBC and BRCA-1 associated breast cancers are sensitive to DNA cross-linking agents such as platinum compounds due to defective DNA repair by homologous recombination. TNBCs are also associated with a high frequency of PTEN loss, which can lead to activation of the mTOR pathway resulting in tumor cell growth and proliferation. mTOR activation can confer resistance to platinum agents, and this phenomenon may be reversible by the addition of an mTOR inhibitor, such as everolimus. A prior phase II single arm trial of carboplatin and everolimus in patients (pts) with advanced TNBC demonstrated good tolerability and preliminary efficacy. Methods: We conducted a phase II, multicenter, randomized trial in pts with advanced TNBC, who had received 0-3 prior lines of therapy. Pts were randomly assigned (in a 2:1 ratio) to carboplatin and everolimus or carboplatin alone. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival (OS), overall response rate (ORR), clinical benefit rate (CBR), and safety. We planned to enroll 72 pts which would provide > 80% power for a one-sided log-rank test at the 5% level of significance, to detect a 2.5 month improvement in median PFS between treatment groups, assuming a median PFS of 2.5 months in the control group. An interim analysis for futility was planned after 36 events with a stopping boundary of P <0.375 for the comparison of PFS, using an Obrien-Fleming spending function. Of note, the trial was stopped earlier than planned based on a sensitivity/tipping point analysis which indicated that terminating the trial 3 months ahead of schedule would have no substantial impact on the primary endpoint. Results: A total of 56 pts were randomized between 2015 and 2022, of whom 36 received carboplatin/everolimus and 20 carboplatin alone. The median age of the population was 62.8 years (range: 33-87) and about 20% of pts had BRCA-1 or BRCA-2 mutations. In the overall population, pts had received a median of 1 (range 1-3) prior line of therapy in the metastatic setting, with 75% of pts receiving prior chemotherapy and 47% prior carboplatin. The median PFS was significantly improved in pts who received carboplatin and everolimus (4.7 months) versus those who received carboplatin alone (2.1 months; HR: 0.37; 95% CI: 0.19-0.72; p=0.0042). Overall survival was 22.1 months in pts on the combination versus 14.4 months on carboplatin alone (HR: 0.73; 95% CI: 0.30-1.72; p=0.3106). CBR was 61% with the combination vs 50% with carboplatin monotherapy, as shown in Table 1. Most common adverse events (AEs) on carboplatin and everolimus included thrombocytopenia (81%), anemia (69%), leukopenia (67%), fluid retention (64%), and neutropenia (61%). Overall, Grade 3/4 events occurred in 75% of pts (83% of pts on combination vs 60% on carboplatin alone) and were primarily anemia (40% vs 17%), thrombocytopenia (47% vs 0%), and neutropenia (20% vs 0%). Of note, there was an increase in thrombocytopenia with the addition of everolimus (All Grades: 81% vs 35%, Grade 3/4: 39% vs 0%). Conclusions: Treatment options for TNBC are limited due to a lack of targeted therapies. The combination of carboplatin and everolimus in this study was associated with a 63% reduction in risk of progression or death in pts with metastatic TNBC. The regimen was well tolerated and provides a promising treatment option for pts with advanced TNBC. Table 1. Results in Patients on Carboplatin and Everolimus versus Carboplatin Alone NE= Not Estimable; 1Unevaluable patients treated as non-responders in CBR and ORR calculations. Citation Format: Rima Patel, Jami Fukui, Paula Klein, Erin Moshier, Charles Shapiro, Anupama Goel, Julie Fasano, Theresa Shao, Aarti Bhardwaj, Rita Vaccaro, Gargi Atul Joshi, Joseph Sparano, Amy Tiersten. A Randomized Phase II Comparison of Single-Agent Carboplatin versus the Combination of Carboplatin and Everolimus for the Treatment of Advanced Triple Negative Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-06-07.

Abstract PO2-08-07: Evaluating chemotherapy receipt and candidacy for PARP inhibitors in germline BRCA1/2 carriers with early and locally advanced breast cancer

Abstract Introduction: While enhanced breast screening of germline BRCA1/2 carriers results in earlier stage at diagnosis, the impact of tumour biology and BRCA mutation on chemotherapy receipt in early stage disease remains understudied. Methods: We retrospectively reviewed treatment administered following a first diagnosis of BRCA1/2-associated breast cancer between 2003-2023 at our institution. Chemotherapy receipt (neoadjuvant or adjuvant) was evaluated according to tumor size, biologic subtype, and BRCA mutation. Current guidelines for PARP inhibitor use were applied to estimate the proportion of affected BRCA1/2 carriers that would be deemed eligible for targeted therapy in the future. Results: Overall, 251 affected BRCA1/2 carriers were included; 137 (54.6%) BRCA1 (median age 40 years, range 19-72) and 114 (45.4%) BRCA2 (median age 43, range, 24-80 years). Chemotherapy was administered in 70.1% of index breast cancer cases and was significantly associated with clinical tumor size (36.7% T1a-T1b, 90.9% T1c, 95.2% T2, 95.3% T3-T4, p< 0.001), nodal status (71.8% cN0 vs. 100% cN1-2, p=0.004), and biologic subtype (90.0% TNBC vs. 75.0% ER+HER2-, p=0.02). BRCA1-associated breast cancers were less likely to present with DCIS or T1 tumours (%Tis/T1; 46.7% BRCA1 vs. 70.8% BRCA2, p< 0.001) and more likely to present with triple negative disease (71.4% BRCA1 vs. 24.6% BRCA2, p< 0.001). BRCA1 carriers were more likely to require chemotherapy for index breast cancer (81.8% BRCA1 vs. 56.1% BRCA2, p< 0.001). In subgroup analysis of early stage, T1N0 disease, chemotherapy was administered in 79.0% BRCA1 and 52.2% BRCA2 patients (p=0.03). If recent guidelines incorporating biologic subtype, nodal involvement, and response to neoadjuvant chemotherapy were retrospectively applied to the cohort, 33.6% would be deemed eligible for PARP inhibitors in the adjuvant setting, including 40.9% BRCA1 and 17.5% BRCA2 affected carriers (p < 0.001). Conclusion: Chemotherapy receipt is high in BRCA-associated breast cancers including in early stage, node-negative disease. Overall, one third of affected carriers are expected to be eligible for PARP inhibitors in the adjuvant setting. Future studies exploring how this information may impact decisions around risk-reducing mastectomy are warranted. Citation Format: Stephanie Wong, Carla Apostolova, Amina Ferroum, Basmah Alhassan, Ipshita Prakash, Mark Basik, Karyne Martel, Sarkis Meterissian, David Fleiszer, Nora Wong, Talia Malagon, William Foulkes, Jean-Francois Boileau. Evaluating chemotherapy receipt and candidacy for PARP inhibitors in germline BRCA1/2 carriers with early and locally advanced breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-08-07.

Abstract PO5-09-04: Oncotype DX Breast Recurrence Score® analysis in early-stage breast cancer associated with CHEK2, ATM and PALB2 germline pathogenic variants

Abstract Background: The 21-gene assay (Oncotype DX Recurrence Score, RS) is the only clinically validated assay to determine the prognosis in hormone-positive, HER2-negative breast cancer (BC) patients treated with endocrine therapy alone by predicting locoregional and distant recurrence. Outcomes of Oncotype RS in BRCA-associated BC has been studied previously, but the results of RS analysis in BC patients with the other BC susceptibility genes have not been documented. This study evaluates the clinical and pathological characteristics of BC patients with ATM, CHEK2 and PALB2 germline pathogenic variants (PV). Methods: Patients with invasive hormone-positive, HER2-negative BC who have had Oncotype DX Breast Recurrence Score® testing and who underwent genetic testing in the Breast Medical Oncology and the Breast Clinical Cancer Genetics Clinic at the University of Texas MD Anderson Cancer Center (MDACC) were identified from the prospectively maintained research database. Clinical and tumor characteristics were analyzed using descriptive statistics. Results: Between 1996 and June 2023, 5652 patients with Oncotype RS were included in this analysis. Amongst those 828 BC patients had genetic testing and 81 patients were found to have a pathogenic variant: 17 patients with a CHEK2 mutation, 10 patients with an ATM mutation, and 18 patients with a PALB2 mutation. Among patients with CHEK2 PV, median Oncotype RS was 17 (5–32) overall, 21 (13–32) for patients age < 50, and 14.5 (5–28) for patients age ≥50 (p= 0.2). Among patients with ATM PV, median RS was 16.5 (3–54) overall, 25 (10–54) for patients age < 50, and 14.5 (3–29) for patients age ≥50 (p= 0.19). Among patients with PALB2 PV, median RS was 26.5 (15–40) overall, 20 (15–40) for patients age < 50, and 31 (26–37) for patients age ≥50 (p= 0.012). Further patient and tumor characteristics are shown in Table 1. Conclusion: This is a single-institutional cohort of hormone-positive, HER2-negative BC patients who had Oncotype RS and who underwent genetic testing. Further analysis on clinical and tumor pathological characteristics and long-term outcome is ongoing. Table1. Patient and tumor characteristics Citation Format: Fatma Akkoc Mustafayev, Angelica Gutierrez Barrera, Diane Liu, Banu Arun. Oncotype DX Breast Recurrence Score® analysis in early-stage breast cancer associated with CHEK2, ATM and PALB2 germline pathogenic variants [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-09-04.

Abstract PO4-06-06: Clinical Implications of Body Mass Index (BMI) in BRCA-associated Advanced Breast Cancer Patients Treated With PARP (Poly ADP-Ribose Polymerase) Inhibitors

Abstract Background: PARP inhibitors (PARPi) have demonstrated promising results in patients with advanced as well as early breast cancer carrying germline BRCA1/2 pathogenic variants (PV). Although there is increasing attention to the effect of BMI on the outcomes of cancer patients, there is limited data on its effect on BRCA-associated advanced breast cancer patients receiving PARPi therapy. In this report, we evaluate the effect of BMI on the outcomes of advanced breast cancer patients with a BRCA PV and who received PARPi therapy. Methods: Patients with BRCA 1/2 germline PVs who presented to the University of Texas MD Anderson Cancer Center Breast Medical Oncology clinics and were treated with PARPi between 2008-2022 as part of their treatment for metastatic or recurrent disease were included in the analysis. The patients were divided into four groups according to BMI level as follows: underweight (< 18.5 kg/m2), normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2), and obese (≥30 kg/m2). Descriptive statistics, the Kaplan-Meier method, the Cox proportional hazards regression model, and Fisher’s exact test were used to report patient characteristics and outcomes. Progression-free survival (PFS) was calculated from the start of the PARPi therapy to the time of progression or death. Overall survival (OS) was calculated from the start of the PARPi therapy to the time of death of any cause. Results: One hundred and seven patients were treated with PARPi. The median BMI was 25.9 kg/m2 (14.8-61.2). In patients who received ≥2 cycles of PARPi, the overall response rate was 100% in the underweight group (n=4, 3.8%), 65.8% in the normal weight group (n=43, 41%), 64% in the overweight group (n=30, 28.6%), and 58.3% in the obese group (n=28, 26.7%). The median PFS was 5.4 months, 9.2 months, 9 months, and 8.6 months in underweight, normal weight, overweight, and obese patients, respectively. While the obese patients had a better outcome in terms of PFS (p = 0.0288), there was no significant difference observed in OS between BMI groups. Conclusion: In this analysis, we showed that obese patients with BRCA-associated advanced breast cancer had a better PFS. Future studies analyzing body composition parameters in BRCA-associated breast cancer patients treated with PARPi therapy could shed more light on the impact of obesity on outcomes. Citation Format: Fatma Akkoc Mustafayev, Mark Munsell, Rachel Layman, Clinton Yam, Angelica Gutierrez Barrera, Banu Arun. Clinical Implications of Body Mass Index (BMI) in BRCA-associated Advanced Breast Cancer Patients Treated With PARP (Poly ADP-Ribose Polymerase) Inhibitors [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-06-06.

Abstract 7120: Investigating PARP1 selective inhibitor DSB1559 efficacy in BRCA1-associated triple negative breast cancer

Abstract Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) have improved outcomes of BRCA-associated breast cancer. However, toxicity can limit patient response as well as the ability to be combined with other therapeutics. Current PARPi broadly inhibit members of the PARP protein family, however only inhibition of PARP1 is needed for PARPi-mediated cell death. As inhibition of PARP2 is associated with hematological toxicity seen in PARPi patients, selectively inhibiting PARP1 may reduce PARPi toxicity and lead to better outcomes for patients. Here we characterize and test the efficacy of the PARP1 selective inhibitor (PARP1i) DSB1559 compared to Olaparib in BRCA1-associated triple negative breast cancer (TNBC). Methods: NanoBRET, PARylation, and pharmacokinetic/pharmacodynamic assays were performed to examine DSB1559 potency, PARP family selectivity, and in vivo behavior. Immunocompetent FVB/n mice bearing BRCA1-deficient TNBC (CMV-Cre;Brca1f/f;Trp53f/f) tumors were treated daily with PARPi (Olaparib) or PARP1i (DSB1559) for 60 days and followed for survival. CellTiter-Glo and qPCR assays were used to examine DSB1559 effect on cell viability and STING activation, respectively. Results: DSB1559 is a novel and potent PARP1 inhibitor which has superior selectivity for PARP1 compared to Olaparib and PARP1i AZD5305. DSB1559 has highly desirable physico-chemical and in vitro ADME properties, which translate to high oral bioavailability and moderate clearance in rodent PK studies. Additionally, DSB1559 demonstrated superior tumor residence time and tumor/plasma ratio compared to AZD5305. Compared to Olaparib, DSB1559 significantly increased STING activation and reduced cell viability in BRCA1-associated murine TNBC cells. BRCA1-associated TNBC-bearing immune-competent mice treated with DSB1559 had significantly reduced tumor growth and increased overall survival (median survival 74 days) compared to Olaparib (median survival 18 days). Analysis of changes in the tumor microenvironment are ongoing. Conclusions: Taken together, DSB1559 is a highly selective PARP1 inhibitor that demonstrates superior efficacy compared to Olaparib in a BRCA1-associated immune-competent TNBC model. Citation Format: Adam Nelson, Kelly F. Zheng, Carlos Wanderley, Daniel E. Michaud, Phillip M. Cowley, Gillian M. Campbell, Barry E. McGuinness, Alan Wise, Jennifer Guerriero. Investigating PARP1 selective inhibitor DSB1559 efficacy in BRCA1-associated triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7120.

Abstract 2998: Regulation of epidermal growth factor receptor signaling by BRCA1-microRNA 146a network

Abstract Inherited defects in the breast cancer susceptibility gene, BRCA1 are associated with an increased risk for hereditary breast, ovarian, and other cancers. BRCA1-associated basal like breast cancers (BLBCs) are high-grade ductal carcinomas that do not express ER, PR or HER2, but frequently overexpress epidermal growth factor receptor (EGFR/ErbB1/HER1). The EGFR-driven signaling network plays a pivotal role in BLBC pathogenesis. EGFR overexpression is associated with tumor progression and metastasis, resistance to radiation and chemotherapy, and poor prognosis. Growth factor receptors are regulated by multiple miRNAs, each having many targets, coordinately controlling the complex pathways of downstream signaling. We have previously reported a post-transcriptional mechanism by which BRCA1 regulates EGFR expression through the induction of miR-146a and provided a rationale for the development of miR-146a based therapeutic strategies. In addition, we have shown that BRCA1 also exerts regulatory control over dozens of important miRNAs that appear to play a critical role in breast neoplasia. From TCGA analysis, we show that low expression of these miRNAs is associated with distinctively poor overall survival of TNBC patients. Using miR-146a loss or gain of function experiments in vitro, we show that BRCA1 and miR-146a regulate EGFR signaling, stemness, epithelial-to-mesenchymal transition (EMT), extracellular matrix (ECM) remodeling and chemoresistance. Using in vivo mouse models, we demonstrate that miR-146a overexpression delays tumor formation leading to better overall survival. BLBC unlike the other subtypes, lacks targeted therapy approaches making cytotoxic chemotherapy essentially the only option for treatment. Though EGFR inhibitors have been used to treat other cancers, clinical trials for breast cancer have so far been unsuccessful due to poor response rates. Since one miRNA can target multiple genes and regulate multiple signaling pathways, our study provides evidence to suggest that restoring miR-146a could suppress EGFR-RAS-MEK signaling and the other compensatory pathways, providing a targeted therapeutic option for BRCA1 associated BLBC. Citation Format: Easwari Kumaraswamy, Raeann M. Koren Shimak, Sumedha Gunewardena, Karen L. Wendt, Dani Alexander, Stacey L. Hembruff, Roy A. Jensen. Regulation of epidermal growth factor receptor signaling by BRCA1-microRNA 146a network [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2998.

Abstract B042: A screen to identify modifiers of BRCA1 protein level for cancer prevention and treatment

Abstract The breast cancer susceptibility gene 1 (BRCA1) is a nuclear phosphoprotein involved in DNA double-strand break (DSB) repair and maintenance of genome stability. A single BRCA1 mutation leads to reduced levels of functional BRCA1 protein, such that DSB repair is compromised. It has been proposed that BRCA1 is a haploinsufficient tumor suppressor gene in some contexts, which when lost accelerates the mutation rate of other critical genes thus increasing neoplastic transformation. BRCA1 expression levels are modified through exogenous exposures, and modulating BRCA1 expression may alter tumour onset, progression, and treatment options. We hypothesize that compounds that increase BRCA1 expression and function may prevent the outgrowth of BRCA1-associated breast cancer. By contrast, compounds that reduce BRCA1 protein level could be used as combination therapries in conjunction with poly-ADP ribose polymerase (PARP) inhibitors. To achieve these goals, we generated BRCA1-reporter cell lines. Using CRISPR-assisted genome editing, we endogenously tagged the BRCA1 protein with HiBiT, an 11 amino acid luminescent tag. BRCA1-targeting was verified by sequencing and immunoblotting, and functional validation was performed with known modulators of BRCA1 expression. Our tests confirmed that HiBiT-tagging allows for sensitive measurement of BRCA1 protein levels, therefore permitting screenability. BRCA1-reporter cells were subsequently used to conduct a pilot screen (64 epigenetic-modifying drugs) and a high-content screen (6,000 compounds). We identified several compounds that modified BRCA1 protein expression (B-score >3*SD). The epigenetic drug library yielded five repressors and two activators, and the high-content screen identified 163 repressors and 12 activators. Validation studies have confirmed that the activator drug, aloxistatin can elevate BRCA1-HiBiT levels in a dose-dependent manner. Additionally, aloxistatin treatment increased BRCA1 expression and function in a panel of breast cells. We have also assessed 9 down-regulators of BRCA1 from the pilot and high-content screens. Each of these nine compounds reduced the expression of BRCA1 protein and synergized with the PARP inhibitor olaparib to inhibit cancer cell growth. Collectively, our ongoing studies suggest that BRCA1 activation may reduce cancer phenotypes and BRCA1 repression can sensitize breast cancer cells to PARP-inhibition and other chemotherapies. Overall, using our reporter cell lines we have identified a number of unique compounds that effectively modify BRCA1 expression and function that may have utility in the treatment and prevention of BRCA1-associated cancers. Citation Format: Erin Sellars, Margarita Savguira, Joanne Kotsopoulos, Leonardo Salmena. A screen to identify modifiers of BRCA1 protein level for cancer prevention and treatment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B042.

Gender-Specific Genetic Predisposition to Breast Cancer: BRCA Genes and Beyond

Among neoplastic diseases, breast cancer (BC) is one of the most influenced by gender. Despite common misconceptions associating BC as a women-only disease, BC can also occur in men. Additionally, transgender individuals may also experience BC. Genetic risk factors play a relevant role in BC predisposition, with important implications in precision prevention and treatment. The genetic architecture of BC susceptibility is similar in women and men, with high-, moderate-, and low-penetrance risk variants; however, some sex-specific features have emerged. Inherited high-penetrance pathogenic variants (PVs) in BRCA1 and BRCA2 genes are the strongest BC genetic risk factor. BRCA1 and BRCA2 PVs are more commonly associated with increased risk of female and male BC, respectively. Notably, BRCA-associated BCs are characterized by sex-specific pathologic features. Recently, next-generation sequencing technologies have helped to provide more insights on the role of moderate-penetrance BC risk variants, particularly in PALB2, CHEK2, and ATM genes, while international collaborative genome-wide association studies have contributed evidence on common low-penetrance BC risk variants, on their combined effect in polygenic models, and on their role as risk modulators in BRCA1/2 PV carriers. Overall, all these studies suggested that the genetic basis of male BC, although similar, may differ from female BC. Evaluating the genetic component of male BC as a distinct entity from female BC is the first step to improve both personalized risk assessment and therapeutic choices of patients of both sexes in order to reach gender equality in BC care. In this review, we summarize the latest research in the field of BC genetic predisposition with a particular focus on similarities and differences in male and female BC, and we also discuss the implications, challenges, and open issues that surround the establishment of a gender-oriented clinical management for BC.

Abstract A006: Characterizing antitumor response of PARP inhibitor and synergy of docetaxel and PARP Inhibitor in BRCA1/2 mutant TNBC breast cancer PDX models

Abstract Introduction: BRCA1 and BRCA2 are tumor suppressor genes that produce proteins which help repair damaged DNA. Even though FDA-approved PARPi, like olaparib or talazoparib, are successful in some BRCA-associated breast cancers, the occurrence of PARPi’s resistance remains a therapeutic challenge. In this study, we investigated the antitumor response of olaparib and the synergy of docetaxel and olaparib in a cohort of TNBC PDX models which were originated from patients with different BRCA1/2 mutation status. Methods: An efficacy study was conducted in 6 TNBC PDX models established subcutaneously in immunodeficient mice. Germline mutations of BRCA1/2 genes in the PDX models were determined by both RNA and whole exome sequencing. Animals were treated with docetaxel, olaparib, or olaparib plus docetaxel. The tumor growth inhibition (TGI) ratio of each treatment group was calculated at the end point, and the synergy score, defined as the difference between observed and expected TGI of the combination group in percentage, was determined. Results: In vivo efficacy responses to olaparib varied across the panel of TNBC PDX models. BR9479 (BRAC2 mutant), originated from primary lesion of a chemotherapy-naïve patient, was sensitive to olaparib, with 87% TGI, while the BR9480 (BRAC2 mutant), which originated from the skin metastases lesion of the same patient after AC-T treatment, was completely resistant to olaparib treatment. A comparison of the genome sequences of this pair of models showed a MED12 gene (G1676D) variant, a deleterious mutation, which has been reported to confer resistance to olaparib in BRCA-deficient cells, associated with restoration of both homology repair (HR) and replication fork protection. BR9464, a BRCA1 mutated model with nonsynonymous variants (P871L, E1038G, K1183R) showed limited response to Olaparib with 19% TGI. While BR9457 with additional deleterious variants (D693N, Q356R) in BRCA1 showed 41% TGI to olaparib. Partial response to the PARPi was also observed in BR9465 (68% TGI) and BR9493 (39% TGI) carrying the PARP1 missense variant (V762A), which is associated with decreased PARylation activity. Chemotherapy induces DNA lesions and cytotoxicity in cancer cells, and when combined with inhibiting PARP1 DNA repair, the effectiveness of therapies can be increased. Similar to the olaparib single treatment, the combination of docetaxel and olaparib showed different synergies depending on the BRAC mutation status. Indeed, models BR9457 and BR9464 that carry BRCA1 (p.S1634G; p.K1183R; p.E1038G; p.P871L) variants and BRCA2 (p.V2466A) variants simultaneously present enhanced synergy with the combination treatment compared with other models. Conclusion: The results presented in this study indicate complicated mechanisms related to the PARPi treatment response as well as potential synergy dependent on the different BRAC1/2 mutation status. The series of established BRCA-mutant breast cancer PDX models with different characters provides a valuable preclinical platform for the development of novel therapeutic strategies. Citation Format: Jinxi Wang, Leilei Chen, Likun Zhang, Binchen Mao, Sheng Guo, Ludovic Bourre, Jingjing Wang, Rekha Pal. Characterizing antitumor response of PARP inhibitor and synergy of docetaxel and PARP Inhibitor in BRCA1/2 mutant TNBC breast cancer PDX models [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A006.

Current approaches to systemic treatment of <i>BRCA</i>-associated triple-negative breast cancer

BRCA-associated triple-negative breast cancer (TNBC) is characterized by high sensitivity to DNA-damaging cytotoxic drugs. The use of well-known BRCA1/2-specific antitumor agents – platinum derivatives and PARP inhibitors – has been discussed for a long time in the context of the treatment of metastatic BRCA-associated TNBC. Neoadjuvant regimens based on the use of anthracyclines and taxanes are the standard of drug therapy for primary BRCA-associated breast cancer. At present, there are few data regarding the addition of platinum drugs to anthracycline-taxane neoadjuvant chemotherapy in the treatment of primary BRCA-associated TNBC. This review details the various treatment options for both primary and metastatic BRCA-associated TNBC. It has been shown that the development of new strategies for the neoadjuvant chemotherapy of patients with primary BRCA-associated TNBC is an urgent clinical need to reduce the risks of recurrence and progression.

Performance of a RAD51-based functional HRD test on paraffin-embedded breast cancer tissue

PurposeBRCA-deficient breast cancers (BC) are highly sensitive to platinum-based chemotherapy and PARP inhibitors due to their deficiency in the homologous recombination (HR) pathway. However, HR deficiency (HRD) extends beyond BRCA-associated BC, highlighting the need for a sensitive method to enrich for HRD tumors in an alternative way. A promising approach is the use of functional HRD tests which evaluate the HR capability of tumor cells by measuring RAD51 protein accumulation at DNA damage sites. This study aims to evaluate the performance of a functional RAD51-based HRD test for the identification of HRD BC.MethodsThe functional HR status of 63 diagnostic formalin-fixed paraffin-embedded (FFPE) BC samples was determined by applying the RAD51-FFPE test. Samples were screened for the presence of (epi)genetic defects in HR and matching tumor samples were analyzed with the RECAP test, which requires ex vivo irradiated fresh tumor tissue on the premise that the HRD status as determined by the RECAP test faithfully represented the functional HR status.ResultsThe RAD51-FFPE test identified 23 (37%) of the tumors as HRD, including three tumors with pathogenic variants in BRCA1/2. The RAD51-FFPE test showed a sensitivity of 88% and a specificity of 76% in determining the HR-class as defined by the RECAP test.ConclusionGiven its high sensitivity and compatibility with FFPE samples, the RAD51-FFPE test holds great potential to enrich for HRD tumors, including those associated with BRCA-deficiency. This potential extends to situations where DNA-based testing may be challenging or not easily accessible in routine clinical practice. This is particularly important considering the potential implications for treatment decisions and patient stratification.

Surgical options for patients with early-stage breast cancer and pathogenic germline variants: an oncologist perspectives.

Breast cancer continues to be the most common cancer diagnosed among women worldwide. Family history of breast cancer is frequently encountered, and 5-15% of patients may carry inherited pathogenic germline variants, identification of which can be helpful for both; patients themselves and their unaffected close relatives. The availability and affordability of molecular diagnostics, like next generation sequencing (NGS), had resulted in wider adoption of such technologies to detect pathogenic variants of cancer-predisposing genes. International guidelines had recently broadened the indications for germline genetic testing to include much more patients, and also expanded the testing to include multi-gene panels, while some professional societies are calling for universal testing of all newly diagnosed patients with breast cancer, regardless of their age, personal or family history. The risk of experiencing a contralateral breast cancer (CBC) or ipsilateral recurrence, is well known. Such risk is highest with variants like BRCA1 and BRCA2, but less well-studied with other less common variants. The optimal local therapy for women with BRCA-associated breast cancer remains controversial, but tends to be aggressive and may involve bilateral mastectomies, which may not have any survival advantage. Additionally, surgical management of unaffected women, known to carry a pathogenic cancer-predisposing gene, may vary from surveillance to bilateral mastectomies, too. The oncological safety, and the higher satisfaction of unaffected women and patients with new surgical techniques, like the skin-sparing (SSM) and nipple-sparing (NSM) mastectomies, eased up the process of counselling. In this review, we address the oncological safety of less aggressive surgical options for both; patients and unaffected carriers.

Experience of using talazoparib in the aggressive course of BRCA2-associated triple-negative breast cancer: a clinical observation

The median overall survival for patients with metastatic triple-negative breast cancer is about 12-14 months. Chemotherapy has been the only treatment option for this tumour subtype for a long time, irrespective of immunological and genetic characteristics. Straightforward therapy algorithms have not been defined, and the optimum sequencing of chemotherapy regimens is left to the discretion of the attending physician. Today, impressive findings from clinical studies on the use of immunotherapy and targeted therapy for cancer using PARP inhibitors reflect in current guidelines, raising the chances of patients to prolong life and maintain its high quality. Thus, the use of immunotherapy as first-line treatment of PD-L1-positive tumours allowed to significantly increase the overall survival of patients for the first time in many years. And the use of PARP inhibitors in carriers of BRCA1/2 germline mutations not only significantly prolongs progression-free survival, but also improves quality of life versus standard chemotherapy regimens. The benefit is also observed in patients with an aggressive course of the disease such as damage to the visceral organs and the central nervous system. The presence of BRCA1/2 germline mutations in the genes, damage to the CNS and visceral organs is associated with an extremely unfavourable prognosis and a significant decline in life expectancy. However, a high-quality diagnosis before initiation of treatment, creating proper treatment plans and the use of modern opportunities can improve the outcomes of treatment. The article discusses possible treatment options for metastatic TNBC, reflects current guidelines on the use of immuno- and targeted therapy. A clinical case report of the treatment of a patient with a significantly aggravated history and an aggressive course of TNBC is presented. The patient with visceral metastases, brain damage and early progression after primary treatment has been receiving therapy for two years, while maintaining a satisfactory quality of life.

Contralateral breast cancer risk in patients with breast cancer and a germline-BRCA1/2 pathogenic variant undergoing radiation.

Radiation-induced secondary breast cancer (BC) may be a concern after radiation therapy (RT) for primary breast cancer (PBC), especially in young patients with germline (g)BRCA-associated BC who already have high contralateral BC (CBC) risk and potentially increased genetic susceptibility to radiation. We sought to investigate whether adjuvant RT for PBC increases the risk of CBC in patients with gBRCA1/2-associated BC. The gBRCA1/2 pathogenic variant carriers diagnosed with PBC were selected from the prospective International BRCA1/2 Carrier Cohort Study. We used multivariable Cox proportional hazards models to investigate the association between RT (yes vs no) and CBC risk. We further stratified for BRCA status and age at PBC diagnosis (<40 and >40 years). Statistical significance tests were 2-sided. Of 3602 eligible patients, 2297 (64%) received adjuvant RT. Median follow-up was 9.6 years. The RT group had more patients with stage III PBC than the non-RT group (15% vs 3%, P < .001), received chemotherapy more often (81% vs 70%, P < .001), and received endocrine therapy more often (50% vs 35%, P < .001). The RT group had an increased CBC risk compared with the non-RT group (adjusted hazard ratio [HR] = 1.44; 95% confidence interval [CI] = 1.12 to 1.86). Statistical significance was observed in gBRCA2 (HR = 1.77; 95% CI = 1.13 to 2.77) but not in gBRCA1 pathogenic variant carriers (HR = 1.29; 95% CI = 0.93 to 1.77; P = .39 for interaction). In the combined gBRCA1/2 group, patients irradiated when they were younger than or older than 40 years of age at PBC diagnosis showed similar risks (HR = 1.38; 95% CI = 0.93 to 2.04 and HR = 1.56; 95% CI = 1.11 to 2.19, respectively). RT regimens minimizing contralateral breast dose should be considered in gBRCA1/2 pathogenic variant carriers.

In Silico Identification of a BRCA1:miR-29:DNMT3 Axis Involved in the Control of Hormone Receptors in BRCA1-Associated Breast Cancers.

Germline inactivating mutations in the BRCA1 gene lead to an increased lifetime risk of ovarian and breast cancer (BC). Most BRCA1-associated BC are triple-negative tumors (TNBC), aggressive forms of BC characterized by a lack of expression of estrogen and progesterone hormone receptors (HR) and HER2. How BRCA1 inactivation may favor the development of such a specific BC phenotype remains to be elucidated. To address this question, we focused on the role of miRNAs and their networks in mediating BRCA1 functions. miRNA, mRNA, and methylation data were retrieved from the BRCA cohort of the TCGA project. The cohort was divided into a discovery set (Hi-TCGA) and a validation set (GA-TCGA) based on the platform used for miRNA analyses. The METABRIC, GSE81002, and GSE59248 studies were used as additional validation data sets. BCs were differentiated into BRCA1-like and non-BRCA1-like based on an established signature of BRCA1 pathway inactivation. Differential expression of miRNAs, gene enrichment analysis, functional annotation, and methylation correlation analyses were performed. The miRNAs downregulated in BRCA1-associated BC were identified by comparing the miRNome of BRCA1-like with non-BRCA1-like tumors from the Hi-TCGA discovery cohort. miRNAs:gene-target anticorrelation analyses were then performed. The target genes of miRNAs downregulated in the Hi-TCGA series were enriched in the BRCA1-like tumors from the GA-TCGA and METABRIC validation data sets. Functional annotation of these genes revealed an over-representation of several biological processes ascribable to BRCA1 activity. The enrichment of genes related to DNA methylation was particularly intriguing, as this is an aspect of BRCA1 functions that has been poorly explored. We then focused on the miR-29:DNA methyltransferase network and showed that the miR-29 family, which was downregulated in BRCA1-like tumors, was associated with poor prognosis in these BCs and inversely correlated with the expression of the DNA methyltransferases DNMT3A and DNMT3B. This, in turn, correlated with the methylation extent of the promoter of HR genes. These results suggest that BRCA1 may control the expression of HR via a miR-29:DNMT3:HR axis and that disruption of this network may contribute to the receptor negative phenotype of tumors with dysfunctional BRCA1.

Pathologic complete response after neoadjuvant systemic therapy for breast cancer in BRCA mutation carriers and noncarriers.

544 Background: Distinct pathological characteristics and mutational signatures in BRCA-associated breast cancers may result in differential response to chemotherapy but understanding of treatment response after neoadjuvant chemotherapy (NAC) is limited. We describe a single-institutional experience to compare rates of pathologic complete response (pCR) after NAC in BRCA carriers (g BRCA1/2) and noncarriers. Methods: From 11/2013 to 01/2022, 1426 consecutive women with clinical stage I-III breast cancer were treated with NAC followed by surgery. Baseline disease characteristics were compared between g BRCA1/2 and noncarriers using two-sample non-parametric tests. Conditional logistic regression was used to evaluate the association between BRCA status and pCR (i.e., ypT0/is pN0) adjusting for variables selected using backward elimination. Results: 92 (6.5%) and 73 (5.1%) had deleterious mutations in BRCA1 and BRCA2, respectively. Compared to noncarriers, g BRCA1/2 were younger (p&lt;0.001) with clinical T1 (p=0.002) and triple negative disease (TN) (57% vs 25% noncarriers, p&lt;0.001). Almost all patients received doxorubicin/cyclophosphamide/paclitaxel therapy (93%) with g BRCA1/2 more likely to receive carboplatin (p&lt;0.001). pCR rate was 42% of g BRCA1, 21% of g BRCA2, and 26% of noncarriers (p=0.001). Among clinically node positive (cN+) patients, nodal pCR was higher in g BRCA1/2 compared to noncarriers (53/96 (55%) vs 371/856 (43%), p=0.012). This difference was seen in ER+/HER2- (36% gBRCA1/2 vs 20% noncarriers; p=0.027) and TN subtypes (79% g BRCA1/2 vs 45% noncarriers; p&lt;0.001). Poorly differentiated tumors (p&lt;0.001), cN+ (p=0.010), lower cT stage (p=0.028), ductal histology (p&lt;0.001), TN and HER2+ receptor status (p&lt;0.001), absence of lymphovascular invasion (p&lt;0.001), carboplatin receipt (p=0.041), and BRCA1 status (p=0.001) were also associated with pCR on univariate analysis. After adjusting for differentiation and molecular subtype, BRCA1 status remained independently associated with pCR. Conclusions: g BRCA1 undergoing NAC have higher pCR rates relative to g BRCA2 and patients with sporadic disease. Across breast cancer subtypes, g BRCA1/2 more frequently converted to pN0. Defining biological mechanism for these findings would allow customization of treatment based on germline genetics. [Table: see text]

P154 Characteristics and prognosis of BRCA-associated breast cancers: Results from a single-center observational study in Thailand

P154 Characteristics and prognosis of BRCA-associated breast cancers: Results from a single-center observational study in Thailand

Abstract ED2-3: Hormonal exposure and risk in BRCA1/2 carriers

Abstract Women who inherit a pathogenic variant (mutation hereafter) in the BRCA1 or BRCA2 geneface extremely high lifetime risks of developing breast and ovarian (or fallopian tube) cancer. More than two decades since the discovery of these genes, and primary prevention with bilateral mastectomy and salpingo-oophorectomy remain the most effective options to manage cancer risk in this population. Understanding the impact of exogenous hormone use is important for both the clinical management of high-risk women and for furthering our knowledge of the pathogenesis of BRCA-associated disease. In this session, I will review the current epidemiologic data surrounding the role of exogenous (anti)hormone use on BRCA-cancer risk. Specifically, I will discuss the role of tamoxifen in preventing BRCA-associated breast cancer and I will describe whether use of oral contraceptives or hormone replacement therapy (HRT) increase the risk of breast cancer. Where possible, I will present data by gene mutation. Potential associations with the risk of ovarian cancer will also be referred to, given that managing BRCA-cancer risks is a balancing act. Finally, I will review how the epidemiologic information has contributed to the discovery of novel targets for the non-surgical prevention of BRCA1-associated breast cancer and gaps in the literature to be addressed in future research. Citation Format: Joanne Kotsopoulos. Hormonal exposure and risk in BRCA1/2 carriers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr ED2-3.

Distinct breast cancer phenotypes in BRCA 1/2 carriers based on ER status.

BRCA1/2 genes are the two main genes associated with hereditary breast cancers (BC). In the present study, we explore clinical and molecular characteristics of BRCA-associated BC in relation to estrogen receptor (ER) status. Three BC databases (DB) were evaluated: (i) Hadassah oncogenetics (n = 4826); (ii) METABRIC (n = 1980), and (iii) Nick-Zainal (n = 560). We evaluated age at diagnosis in BRCA positive (BP) and BRCA negative (BN) patients,and tested for mutational signature differences in cohort iii. mRNA differential expression analysis(DEA) and pathway analysis were performed in cohort ii. Age at diagnosis was lower in BP vs. BN tumors in all cohorts in the ER- group, and only in cohort i for the ER + group. Signature 3 was universal in BP BC, whereas several signatures were associated with ER status.Pathway analysis was performed between BP&BN, and was significant only in ER- tumors: the major activated pathways involved cancer-related processes and were highly significant. The most significant pathway was estrogen-mediated S-phase entry and the most activated upstream regulator was ERBB2. Signature 3 was universal for all BP BC, while other signatures were associated with ER status. ER + BP& BN show similar genomic characteristics, ER- BP differed markedly from BN. This suggests that the initial carcinogenic process is universal for all BRCA carriers, but further insults lead to the development of two genomically distinct subtypes ER- and ER + . This may shed light on possible mechanisms involved in BP and carry preventive and therapeutic implications.