Germline Mutations In BRCA1 Research Articles

Niraparib maintenance therapy using an individualised starting dose in patients with platinum-sensitive recurrent ovarian cancer (NORA): final overall survival analysis of a phase 3 randomised, placebo-controlled trial

Niraparib significantly prolonged progression-free survival versus placebo in patients with platinum-sensitive, recurrent ovarian cancer (PSROC), regardless of germline BRCA mutation (gBRCAm) status, in NORA. This analysis reports final data on overall survival (OS). This randomised, double-blind, placebo-controlled, phase 3 trial enrolled patients across 30 centres in China between 26 September 2017 and 2 February 2019 (clinicaltrials.gov, NCT03705156). Eligible patients had histologically confirmed, recurrent, (predominantly) high-grade serous epithelial ovarian cancer, fallopian tube carcinoma, or primary peritoneal carcinoma (no histological restrictions for those with gBRCAm) and had received ≥2 prior lines of platinum-based chemotherapy. Patients were randomised (2:1) to receive niraparib or placebo, with stratification by gBRCAm status, time to recurrence following penultimate platinum-based chemotherapy, and response to last platinum-based chemotherapy. Following a protocol amendment, the starting dose was individualised: 200mg/day for patients with bodyweight <77kg and/or platelet count <150×103/μL at baseline and 300mg/day otherwise. OS was a secondary endpoint. Totally, 265 patients were randomised to receive niraparib (n=177) or placebo (n=88), and 249 (94.0%) received an individualised starting dose. As of 14 August 2023, median follow-up for OS was 57.9 months (IQR, 54.8-61.6). Median OS (95% CI) with niraparib versus placebo was 51.5 (41.4-58.9) versus 47.6 (33.3-not evaluable [NE]) months, with hazard ratio [HR] of 0.86 (95% CI, 0.60-1.23), in the overall population; 56.0 (36.1-NE) versus 47.6 (31.6-NE) months, with HR of 0.86 (95% CI, 0.46-1.58), in patients with gBRCAm; and 46.5 (41.0-NE) versus 46.9 (31.8-NE) months, with HR of 0.87 (95% CI, 0.56-1.35), in those without. No new safety signals were identified, and myelodysplastic syndromes/acute myeloid leukaemia occurred in three (1.7%) niraparib-treated patients. Niraparib maintenance therapy with an individualised starting dose demonstrated a favourable OS trend versus placebo in PSROC patients, regardless of gBRCAm status. Zai Lab (Shanghai) Co., Ltd; National Major Scientific and Technological Special Project for "Significant New Drugs Development" in 2018, China [grant number 2018ZX09736019].

Abstract PO1-18-11: Imaging of tumour microvasculature using high-resolution contrast enhanced ultrasound together with markers of proliferation/angiogenesis/vascular mimicry to characterise response to NACT in TNBC

Abstract Background: In the UK, triple-negative breast cancer (TNBC) comprises 10-15% of breast cancer diagnoses annually. TNBC represents a clinical challenge due to a lack of expression of three treatable drug targets, namely oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER-2). The mainstay of treatment involves the use of neoadjuvant chemotherapy (NACT) followed by surgical excision where up to 50% of patients will achieve a pathological complete response (pCR). The addition of neo-adjuvant immunotherapy may increase the pCR rate to 60%. The presence of lymphatics and blood vessels within/around malignant tumours plays a role in cancer progression as does the formation of new blood vessels (angiogenesis). The vascular endothelial growth factor (VEGF) family and their receptors (VEGFRs) play an important role in angiogenesis as well as promoting the growth and survival of cancer cells. VEGFR is frequently overexpressed in TNBC and promotes changes in vascular endothelial cells, the basement membrane and the surrounding extracellular matrix. Co-expression of epidermal growth factor receptor (EGFR) and VEGFR enhances tumour growth and angiogenesis in an autocrine and paracrine manner. An alternate mechanism for tumour microcirculation in tumours is vasculogenic mimicry (VM). This is distinct from classical tumour angiogenesis. The presence of VM is associated with poor overall survival in breast cancer patients and anti-angiogenic treatment of TNBC may even promote tumour growth, proliferation and metastasis by stimulating VM. Conventional imaging techniques such as B-mode ultrasound and MRI are commonly used to monitor disease response in the breast but have limited accuracy in predicting pCR or residual disease. High-resolution contrast-enhanced ultrasound (HRCEUS) may offer a more accurate test to monitor TNBC response to NACT. This method utilises intravenously injected microbubbles, which consist of a gas core with an outer shell of lipid/albumin to image tumour microvasculature as well as gross tumour morphology. Trial Design: Single-centre study to evaluate HRCEUS to image the microvasculature of TNBC tumours in patients undergoing (NACT) and correlate imaging results with established markers of angiogenesis, proliferation and vasculogenic mimicry. Eligibility Criteria: Female, 18 to 60 years, histologically confirmed invasive TNBC with planned NACT, able to consent and in the Investigator’s opinion, adhering to the trial recommendations and governance. Aims: To investigate if imaging changes in the tumour microvasculature indicate a response to NACT and are reflected in the expression of proliferative markers. To determine whether changes in the tumour microvasculature and disease response are driven by angiogenesis +/- VM. To investigate whether overall disease response and changes in the microvasculature are influenced by the basal type phenotype or germline mutations in BRCA 1/2. Investigate patient satisfaction with the contrast ultrasound test. Statistical Methods: Quantify HRCEUS imaging characteristics of microvasculature at 3 treatment points. Compare this with the results of conventional imaging and the histopathological results of surgical excision at the end of NACT. Quantify immunohistochemical markers of angiogenesis, proliferation and VM at three treatment points and compare this with HRCEUS. Determine phenotype of all cases using immunohistochemistry to identify the basal Perform subtype analysis to assess if the basal phenotype is associated with imaging and immunohistochemical changes in the microvasculature during NACT. Test patients for germline BRCA1/2 gene mutations. Perform subtype analysis to assess if germline BRCA1/2 mutations are associated with imaging and immunohistochemical changes in the microvasculature during NACT. Present accrual (2 patients) and target accrual (5 patients) Contact details: j.rait@nhs.net Citation Format: Jaideep Rait, Michelle Garrett, Catherine Harper-Wynne, Sonia Saw, Mengxing Tang, Priya Palanisamy, Matthieu TOULEMONDE, Karina Cox. Imaging of tumour microvasculature using high-resolution contrast enhanced ultrasound together with markers of proliferation/angiogenesis/vascular mimicry to characterise response to NACT in TNBC [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 PO1-18-11.

Abstract PO2-17-06: Real world treatment patterns and clinical outcomes by germline BRCA (gBRCA) mutation status in patients with HER2-negative early breast cancer in the US community oncology setting: a retrospective observational chart-review study

Abstract Background: Women with early-stage breast cancer (eBC) who have inherited BRCA1 or BRCA2 mutations (gBRCAm) are typically diagnosed at a younger age and often require more intensive treatment. In the randomized, double-blind OlympiA trial of HER2-negative (HER2–) gBRCAm patients, olaparib, a targeted poly (ADP-ribose) polymerase inhibitor (PARPi), significantly improved invasive disease free survival (IDFS), distant disease free survival (DDFS) and overall survival (OS) and was subsequently approved for adjuvant treatment of gBRCAm HER2– high-risk eBC patients. This study examined the real-world patient characteristics, treatment patterns and clinical outcomes by gBRCA status among patients with HER2– eBC in a US community oncology setting prior to olaparib US approval for treatment of eBC. Methods: This retrospective observational study used chart review data from The US Oncology Network's iKnowMed database to examine adult patients diagnosed with HER2– eBC (stage I-III) initiating systemic neoadjuvant or adjuvant therapy with chemotherapy and/or endocrine therapy between January 1, 2012 and December 31, 2018. Patients with valid gBRCAm test results (all gBRCAm and randomly selected BRCAwt patients) were included and followed through December 31, 2021. Patients were excluded if they had HER2+ tumors and progressed to stage IV within 6 months after initiation of neoadjuvant therapy or were diagnosed with another primary cancer. Descriptive analyses assessed patient characteristics. Kaplan Meier methods and multivariate Cox proportional hazard models (CPHM) were used to evaluate IDFS, DDFS and OS by gBRCA status and by HR+/HER2– or TNBC eBC subsets. Results: Among 298 BC patients meeting initial criteria, 42% had gBRCAm (n=124, 43% hormone receptor positive [HR+], 56% triple-negative BC [TNBC], 1% unknown), and 58% had gBRCAwt (n=174, 74% HR+, 22% TNBC). Median (interquartile) age at surgery was numerically lower in gBRCAm (45 [36,55] years) than gBRCAwt (48 [41,55] years) patients. A numerically higher proportion of gBRCAm patients received neoadjuvant therapy compared with gBRCAwt (Neoadj: gBRCAm 37.1% vs gBRCAwt 12.6%) but the reverse was true for adjuvant (Adj: gBRCAm 42.7% vs gBRCAwt 65.5%) and neoadjuvant + adjuvant use was numerically similar (Neoadj+Adj: gBRCAm 20.1% vs gBRCAwt 21.8%). The majority of TNBC patients received neoadjuvant therapy while the majority of HR+ patients received adjuvant therapy (Neoadj: TNBC 51.4% vs HR+ 6.6%, Adj: TNBC 29.0% vs HR+ 71.4%, Neoadj+Adj: TNBC 19.6% vs HR+ 22.0%). Median IDFS, DDFS, and OS in both study cohorts were not reached. Median follow-up from surgery was &amp;lt; 5 years (overall 59.0 months; gBRCAm 50.6 months; gBRCAwt 61.3 months). At 60 months, in gBRCAm and gBRCAwt respectively, estimated IDFS were 85.5% and 90.9%, estimated DDFS 88.1% and 92.2%, and estimated survival 91.9% and 95.2%. At 60 months, in HR+/HER2– and TNBC respectively, estimated IDFS were 92.4% and 81.2%, estimated DDFS 93.9% and 85.7%, and estimated survival 96.3% and 90.9%. CPHM results showed that risks of invasive disease (HR 1.74; 95% CI 0.83-3.64; p=0.15), distant disease (HR 1.24; 95% CI 0.50-3.07; p=0.65) and death (HR 1.79; 95% CI 0.52-6.13; p=0.353) were similar between gBRCAm and gBRCAwt patients. Between HR+/HER2– and TNBC patients, risks of invasive disease (HR=0.63; 95% CI 0.21-1.89; p=0.41), distant disease (HR=0.42; 95% CI 0.11-1.67; p=0.22) and death (HR 0.48; 95% CI 0.09-2.70; p=0.41) were similar. Conclusions: This real-world chart review study of data through 2021 (before PARPi approval for eBC) with limited follow up of 5 years found that gBRCAm patients had a numerically shorter survival (IDFS, DDFS and OS) than gBRCAwt, but this difference was not statistically significantly different. Given that the follow-up period was too short to draw conclusions, further studies examining clinical outcomes over a longer follow-up period after approval of PARPi may be of interest. Citation Format: Jay Andersen, Jagadeswara Earla, Nicole Fulcher, Juliet Ndukum, Nicholas J Robert, Mark Robson, Weiyan Li, Jaime Mejia. Real world treatment patterns and clinical outcomes by germline BRCA (gBRCA) mutation status in patients with HER2-negative early breast cancer in the US community oncology setting: a retrospective observational chart-review study [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 PO2-17-06.

Abstract PS06-04: The prognostic and predictive impact of circulating tumour DNA (ctDNA) dynamics in patients with metastatic Triple Negative Breast Cancer (TNBC) on olaparib based therapy: Results from Cohort E of the PlasmaMATCH trial

Abstract Background: Early changes in ctDNA levels, ctDNA dynamics, may help identify which patients are responding to therapy earlier than imaging. Few studies have assessed ctDNA dynamics during PARP inhibitor therapy. Here we report paired baseline and early on treatment ctDNA analysis from cohort E of plasmaMATCH, that recruited patients with TNBC to treatment with olaparib (PARP inhibitor) plus ceralasertib (ATR inhibitor). Methods: The plasmaMATCH trial assessed the ability of ctDNA testing to allocate patients to mutation matched treatment cohorts (A-D). Patients with TNBC, and without mutations matching cohorts B-D, were enrolled on cohort E. Samples were collected for ctDNA analysis pre-treatment at cycle 1-day1 (C1D1) and cycle 2-day 1 (C2D1). A minimum of 14 days of treatment in the first cycle was required for inclusion in this analysis. Samples were sequenced using error-corrected gene targeted panels (Guardant360, or GuardantOMNI, Guardant Health). Circulating DNA ratio (CDR) was calculated as the ratio of C2D1 ctDNA level to C1D1, pre-specified using the weighted mean of variant allele fractions (AF) of clonal mutations at C1D1, excluding variants with AF &amp;lt; 0.3%, and variants in genes frequently mutated in clonal haematopoesis (GNAS, JAK2, IDH1, IDH2 and ATM). The optimal cut-point for predicting progression free survival (PFS) was assessed as the cut-point with the highest Harrell’s C-index. Results: Of the 75 patients that were enrolled into cohort E, 53 patients had samples sent for paired C1D1-C2D1 ctDNA sequencing, 2 failed sequencing, and all 51 (68%) patients had detectable ctDNA at C1D1. The ctDNA analysis set was representative of the overall enrolled population. The optimal ctDNA dynamics C-index cut-point for predicting PFS was 0 (undetectable ctDNA at C2D1). Median PFS with ctDNA CDR &amp;gt;0 (detectable ctDNA at C2D1) was 4.3 months (95% CI 2.4-5.8), and with undetectable ctDNA was 12 months (95% CI 8-NA) (HR 4.02, 95% CI 1.22-13.23, p=0.01). Splitting patients by median CDR was not predictive (HR=0.98; 95%CI: 0.52-1.82, p=0.94). Confirmed objective response rate was 85.7% (42.1-99.6) in patients with undetectable ctDNA at C2D1, and with detectable ctDNA was 11.4% (3.8-24.6) (OR 4.02, 95% CI 1.22-13.23, p=0.01). Of the 7 patients with undetectable ctDNA at C2D1, one had a BRCA2 germline mutation, and all other patients were wildtype for BRCA1/2 mutations in tumour and germline. All patients with undetectable ctDNA and BRCA1/2 wildtype had a confirmed response.In cohorts A-D (mutation targeted therapies, in predominantly ER positive cancer), the optimal ctDNA dynamics C-index CDR cut-point was 0.165 (HR 3.44, 95%CI: 2.06-5.75, p&amp;lt; 0.001), with median CDR cut-point also highly predictive (HR=2.14, 95%CI:1.36-3.36, p=0.001). Undetectable ctDNA was also strongly predictive (HR=4.41; 95%CI: 1.97-9.87, p&amp;lt; 0.001) in cohort A-D.In cohort E, a significant association was found between baseline ctDNA and PFS, with an optimal C-index cutpoint of 6.81% (HR=3.02, 95% CI: 1.39-6.56, p=0.001). Median PFS for baseline ctDNA ≤ 6.81% was 10.2 months (95% CI 3.7-17.2), and for baseline ctDNA &amp;gt;6.81% was 4.4 months (95% CI 2.2-5.5). Conclusions: ‘Clearance’ of ctDNA to become undetectable at C2D1 identified sporadic TNBC patients who benefited from olaparib and ceralasertib. Although ‘clearance’ of ctDNA was associated with good outcome on olaparib plus ceralasertib, median CDR was not predictive of treatment benefit. This contrasts the results of ctDNA dynamic assessment of cohort A-D, where median CDR was highly predictive of treatment benefit. ctDNA dynamic assessment may differ between mutation targeted therapies (cohorts A-D) that induce cell-cycle arrest, and PARP inhibitors (cohort E) that inhibit DNA repair mechanisms. Implementing ctDNA dynamics into clinical trials and care may require distinct analysis for different therapies. Citation Format: Iseult Browne, Javier Pascual, Rosalind Cutts, Belinda Kingston, Sarah Hrebien, Lucy Kilburn, Alex Pearson, Laura Moretti, Andrew Wardley, Iain Macpherson, Richard Baird, Rebecca Roylance, Iris Faull, Kimberly C Banks, Isaac Garcia-Murillas, Judith Bliss, Alistair Ring, Nicholas Turner. The prognostic and predictive impact of circulating tumour DNA (ctDNA) dynamics in patients with metastatic Triple Negative Breast Cancer (TNBC) on olaparib based therapy: Results from Cohort E of the PlasmaMATCH trial [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 PS06-04.

Abstract PO1-16-10: BRCA mutated Male Breast Cancer, hallmarks of a distinct disease. Data from the Spanish Male Breast Cancer Registry (GEICAM/2016-04)

Abstract Background: Male breast cancer (MBC) accounts for approximately 0.25% of all male cancers and &amp;lt; 1% of all BCs. Its incidence is increasing by 1.1% per year. Most population studies indicate that 10-15% of MBC patients (pts) have a germline BRCA2 mutation (BRCA2 mut). Around 5-10% of BRCA2mut male carriers will develop BC at their lives. Preliminary evidence suggests that BRCA2mut MBC pts tend to have a more aggressive disease. Here we present comparative series of MBC with and without BRCA to gain insight on differences between both groups. Methods: GEICAM/2016-04 (NCT03800355) is a retrospective, observational study which includes data from MBC pts diagnosed between 2000 and 2019 throughout Spain. This analysis includes the 1st unselected 186 pts included in the study, who had BRCA1/2 genes mutational status assessed within clinical practice. BC clinical subtypes are defined: luminal (HR+, HER2-), Triple Negative (TN) (HR-, HER2-), and HER2+ (HR+ or HR-); subtype is unknown in 6% pts. Results: 186 validated pts with BRCA1/2 testing were identified, representing the 24% of pts available in the database at the cut-off date (6-Mar-2023). 36 (19%) pts had germline BRCA1/2 mut (4 pts in BRCA1, 31 pts in BRCA 2 and 1 pt in both BRCA1 and BRCA2), and 150 (81%) pts had BRCA1/2 wild type (wt) or a variant of uncertain significance (VUS)/unknown (UK). Median age at BC diagnosis was 62 (34-87) years, 98% pts were Caucasian, and the median body mass index was 27 (18-46) Kg/m2 (overweight). Prior cancer history was reported in 6% BRCA1/2mut BC pts and 11% BRCA1/2wt or vus/uk, and family history included: 56% BC, 8% ovarian cancer, and 14% prostate cancer (PC). PC as part of prior medical history, cancer family history, and 2nd non-breast primary malignancy, was most frequent in BRCA1/2wt or vus/uk pts, with no statistical differences. At first diagnosis, stages III-IV were higher in BRCA1/2mut pts (28% vs. 17%, p=0.0093). Morphologically, invasive carcinoma of no special type (NST) was the most common pattern (92% in BRCA1/2mut vs. 86% in BRCA1/2wt or vus/uk), and lobular invasive carcinoma was not reported up-to-date. Histological grade 2 was the most frequent (54%), but grade 3 was present in 17/36 BRCA1/2mut pts. 88% pts received adjuvant treatment, 7% (neo-)adjuvant, 2% neoadjuvant and 3% did not receive any systemic therapy. Breast conserving surgery was performed in 4% (5/140) BRCA1/2wt or vus/uk EBC pts, and mastectomy was performed in 55% (n=6/11) de novo metastatic pts. In the advanced setting (n=38), visceral lesions were more frequent in BRCA1/2mut pts. Additionally, 92% BRCA1/2mut pts had ≤ 3 organs involved while one third of BRCA1/2wt or vus/uk pts had ≥ 4 metastatic locations. With a median follow-up of 64 months (mo.), median iDFS and DDFS were higher, but not statistically significant, in BRCA1/2wt or vus/uk pts vs. BRCA1/2mut pts. In advanced setting, median PFS to 1L-3L do not show statistically significant differences between both groups. Regarding OS, no differences were also observed, but the median values were not reached. Further detailed information according to BRCA1/2 mutational status and BC subtypes is included in the table below. Conclusions: In this subset analysis of GEICAM/2016-04, BRCA1/2mut pts had some features of worse prognosis, with a more prevalent de novo metastatic disease. No statistically significant differences were observed in outcomes in both early-stage and advanced setting vs. BRCA1/2wt or vus/uk pts. &amp;lt;graphic&amp;gt; Citation Format: Noelia Martínez-Jáñez, Purificación Martínez, Cristina Hernando, Sabela Recalde, Alfonso Sánchez, David Morales, Marta Santisteban, Isaura Fernández, Sonia Del Barco, Esther Zamora, Vega Iranzo, Tamara Martos, Eduardo Martínez-de Dueñas, Silvia Antolin Novoa, Severina Domínguez, Paula Domínguez, Mª José Echarri, Ana Santaballa Bertrán, Xavier Mira, Andrea Blasco, Susana Bezares, Ander Urriticoechea. BRCA mutated Male Breast Cancer, hallmarks of a distinct disease. Data from the Spanish Male Breast Cancer Registry (GEICAM/2016-04) [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 PO1-16-10.

Abstract PS04-02: BRCA testing and PARP inhibitor utilization in real-world HER2-negative metastatic breast cancer

Abstract Background: PARP inhibitors (PARPi) have demonstrated progression-free survival benefits vs. chemotherapy in patients (pts) with metastatic breast cancer (mBC) and germline BRCA mutations (gBRCAm). NCCN guidelines recommend that all pts with mBC are offered gBRCAm testing to aid in systemic treatment decisions with PARPi. Understanding real-world gBRCAm testing patterns and PARPi use would be beneficial for improving clinical outcomes of pts with gBRCAm mBC. Methods: This retrospective cohort study identified pts ≥ 18 years old with HER2-negative mBC, diagnosed from 2014 to 2022 (US Flatiron Electronic Health Record database). gBRCAm testing patterns in mBC over time were examined by BC subtype (hormone receptor-positive [HR+] or triple-negative breast cancer [TNBC]) and disease stage at diagnosis [de novo or recurrent]). Timing of gBRCAm testing and subsequent initiation of first-line or later PARPi in pts with gBRCAm HR+ and TNBC mBC was assessed in pts diagnosed after 2018 when PARPi were approved in mBC. Prevalence of gBRCAm was calculated overall and by mBC subtype. Demographic and clinical characteristics were described by gBRCAm testing and PARPi initiation (yes/no). Real-world overall survival (OS) by PARPi use since mBC diagnosis was estimated using the Kaplan-Meier method and a log-rank test. Results: Of 15,006 total pts, 4654 (31.0%) had a gBRCAm test. Compared with pts who were not tested, gBRCAm-tested pts were younger at initial mBC diagnosis (median age: 53.5 vs. 62.0 years), had a shorter median disease-free interval before mBC diagnosis (821 vs. 959 days), and were less likely to have de novo mBC (28.0% vs. 31.2%). gBRCAm testing prevalence was 6.1% in the HR+ group (n=11,945) and 8.9% in the TNBC group (n=2430). gBRCAm testing rates mostly increased from 2014 to 2022 and were lowest in HR+ tumor subtypes; &amp;lt; 2/3 of all pts had a gBRCAm test from 2020 onwards (Table). Most pts with recurrent mBC (HR+: 68.3%; TNBC: 76.1%) were gBRCAm tested before diagnosis, whereas pts with de novo mBC were tested at a later timepoint ( &amp;gt; 60 days after mBC diagnosis – HR+: 48.3%; TNBC: 38.4%). Of all pts with gBRCAm diagnosed from 2018 onwards (n=187), 44.4% initiated PARPi. A higher proportion of pts with gBRCAm in the TNBC group initiated PARPi (52.9%) than in the HR+ group (42.4%). Pts with gBRCAm in the TNBC group received PARPi earlier than pts with gBRCAm in the HR+ group (mean days from mBC diagnosis to first PARPi use: 173 and 411 days, respectively). Fewer pts with de novo mBC (35.7%) initiated PARPi than pts with recurrent mBC (50.8%). With a median follow-up of 15.3 months, pts with gBRCAm initiated on PARPi had numerically longer median OS (32.3 months [95% CI: 24.2–47.4]) than PARPi non-initiators (21.4 months [95% CI:18.4–43.5]). OS results should be regarded with caution due to the small sample size (n=187). Conclusions: Despite NCCN guideline gBRCAm-testing recommendations, &amp;lt; 2/3 of pts with HER2-negative mBC in our study were gBRCAm tested from 2020 onwards. gBRCAm testing was lower in pts with HR+ disease and was performed at a later timepoint for pts with de novo disease. Wider and timelier implementation of gBRCAm testing to identify pts that could benefit from PARPi is warranted. Fewer pts with gBRCAm who had HR+ tumors or de novo disease received PARPi than pts with TNBC. Our data suggest that pts who initiated PARPi had numerically longer OS than PARPi non-initiators; further research into OS trends and PARPi use in gBRCAm mBC would be of interest. Editorial acknowledgment: Medical writing assistance was provided by Leigh-Ann Booth, Ph.D. from BOLDSCIENCE Inc., funded by AstraZeneca and Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, US Legal entity responsible for the study: AstraZeneca. Funding: This study was supported by AstraZeneca and Merck Sharp &amp; Dohme LLC, a subsidiary of Merck &amp; Co., Inc., Rahway, NJ, US, who are codeveloping olaparib. Table. gBRCAm testing rates over time in pts with HER2-negative mBC HER2-negative mBC is defined as IHC 0, or 1-positive, or IHC2-positive/ISH-negative. *Olaparib approved in mBC; †Olaparib approved in eBC. eBC, early breast cancer; gBRCAm, germline breast cancer gene mutation; HER2, human epidermal growth factor receptor 2; HR, hormone receptor; IHC, immunohistochemistry; ISH, in situ hybridization; mBC, metastatic breast cancer; pt, patient; TNBC, triple-negative breast cancer. Citation Format: Siddhartha Yadav, Sam Hillman, Linlin Luo, Weiyan Li, Jagadeswara Earla, Xiaoqing Xu. BRCA testing and PARP inhibitor utilization in real-world HER2-negative metastatic 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 PS04-02.

Abstract PO3-16-06: Perceptions and experiences of patients and healthcare providers on genetic testing and treatment of early breast cancer: qualitative findings

Abstract Background: Olaparib is approved as adjuvant therapy for high-risk HER2-negative early breast cancer (eBC) patients with germline BRCA mutations (BRCAm). Understanding patients’ preferences for genetic testing and treatment in the context of shared decision-making is needed to support optimal care in eBC. This study elicited the perspectives of patients with eBC and healthcare providers (HCP) treating eBC regarding treatment decision-making, and drivers and barriers to BRCA testing. Methods: Semi-structured interviews were conducted in the United States from Jan-Feb 2023 with women (n=12) diagnosed with eBC from 2017-2021. Community and academic oncologists treating eBC (n=12) and genetic counselors (GCs; n=8) were also interviewed. Patients who were tested (n=7) and untested (n=5) for BRCAm were included. A content and thematic analysis was performed which identified key factors from the data; these analyses provided both a range and common responses that may influence BRCA testing and treatment decisions. Results: BRCA-tested patients considered testing beneficial. In choosing to receive testing, &amp;gt;50% of patients reported HCP recommendation (n=7) and the opportunity to have “all of the information” about their eBC (n=7) as strong influencers. Patients declined genetic testing noting fear around negative impact to their insurance coverage (n=2) or mental health (n=3), or if they did not have family who would benefit from the information. Cost did not strongly influence testing choice. In choosing a treatment, patients sought to maintain their quality of life (QoL) with fewer side effects while minimizing chance of recurrence. They expressed the dual goals of normalcy during treatment, including curtailing side effects that impact QoL, and returning to normalcy after treatment (n=7). Patients were willing to accept unpleasant side effects to have a more effective treatment if those side effects do not severely impact their QoL and the treatment is highly effective (n=9). Side effects that may lead to hospitalization were the least accepted as they disrupt normalcy. HCPs reported that patients eagerly accept testing and face minimal familial or access barriers to testing. HCPs observed that among their non-Medicare patients, testing is usually covered by insurance with minimal out-of-pocket costs, thus alleviating financial constraints observed in previous years. HCPs believe BRCA testing is driven by updated hereditary cancer testing guidelines (e.g., NCCN), lower testing costs, closer collaborations of physicians and genetic counselors, and greater awareness among patients. HCPs reported that they embrace patient-led decision-making in eBC, especially as it relates to patients with BRCAm considering additional prophylactic surgery, and GCs further emphasized patient autonomy. Oncologists mentioned that they discuss risk status starting at diagnosis and these conversations evolve over the patient journey as new information emerges. In HR+ eBC, oncologists offered most patients with BRCAm adjuvant olaparib, which they perceive as well tolerated. In triple-negative eBC, oncologists opted for neoadjuvant Keytruda regimen prior to considering adjuvant olaparib for gBRCAm patients. Conclusions: Patients value information that empowers them to achieve their goals of normalcy and remission that can be achieved by addressing QoL, side effects, and patients' goals of living “normally”. Though prior research highlighted insurance coverage and costs as significant barriers to BRCA testing, results from this study suggest that cost was not a major factor in testing decisions. Prior barriers to testing access have been mitigated making it more available and affordable than in the past, which could be broadly communicated to patients and HCPs to minimize misperception. Citation Format: Jagadeswara Earla, Emily Mulvihill, Josh Lankin, Lauren Howell, Alex Kissling, Weiyan Li, Jaime Mejia. Perceptions and experiences of patients and healthcare providers on genetic testing and treatment of early breast cancer: qualitative findings [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 PO3-16-06.

Abstract PO5-13-02: BRCA mutational profiles of endocrine-resistant breast cancer

Abstract Background Around 75% of breast cancer (BC) patients have tumors expressing the treatment-predictive biomarker estrogen receptor α (ER) and are consequently offered endocrine therapy. One-third of these patients develop endocrine resistance, a majority with tumors that retain ER expression. For most cases, the resistance mechanism is still unknown, but mutational activity is a suggested mechanism. Germline BRCA mutations are well-known in BC and are found in approximately 23% of patients with triple-negative BC and in 5% of patients with ER+ BC. However, less is certain about the somatic variants, though studies have shown prevalences of around 3% in BC. This study aimed to examine the somatic BRCA mutational profiles of endocrine-resistant paired primary and relapse tumors. Methods A retrospective cohort of verified endocrine-resistant BC patients was collected at Karolinska University Hospital in Stockholm, Sweden. Patients diagnosed in 2008-2012 with an ER+ and human epidermal growth factor receptor 2 (HER2) negative primary tumor and a following ER+ and HER2- relapse tumor within five years of ongoing endocrine therapy were included (N=63). DNA was extracted from archived formalin-fixed paraffin-embedded relapse and primary tumor tissue and analyzed by panel sequencing. Tumor-free lymph nodes were used as germline normal samples. Results The analysis showed somatic BRCA mutational activity in 38.1% of the patients. Variants were present in 20.3% of primary tumors and 30.4% of relapse tumors. BRCA1 mutations were present in 11.9% of primary tumors and 21.4% of relapse tumors. BRCA2 variations were, in turn, seen in 11.9% of primary tumors and 14.3% of relapse tumors. The frequency of patients that had alterations in both the primary and relapse tumors was 3.2% for BRCA1 and BRCA2 respectively. Conclusion This study of a unique endocrine-resistant BC cohort shows a high presence and varying distribution of somatic BRCA mutations in both primary and even higher in relapse tumors. These results suggest that mutational testing for possible further treatment decisions may be relevant for patients exhibiting endocrine resistance, especially in the advanced setting. Citation Format: Emelie Karlsson, Caroline Schagerholm, Stephanie Robertson, Hosein Toosi, Emmanouil Sifakis, Johan Hartman. BRCA mutational profiles of endocrine-resistant 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 PO5-13-02.

Abstract PO5-17-06: Prevalence of BRCA Mutations: A Predictive Model in a High-Risk Population of BC Patients at a Tertiary Care Center

Abstract Background: Breast cancer (BC) is a prevalent cancer in Saudi Arabia, with the majority of cases being sporadic. However, 25-30% of cases are associated with hereditary factors. Germline BRCA mutations are the most common mutations linked to hereditary BC predisposition syndromes, with a reported frequency of up to 11% in Saudi Arabia. Methods: This retrospective cohort study was conducted at a single institution in Saudi Arabia. Medical records of BC cases were reviewed where BRCA testing was performed, typically in patients with triple negative BC, hormone-positive (HR+) BC in younger premenopausal patients under the age of 45, or those with a personal or family history of BC. Patients meeting these criteria were diagnosed and treated at a tertiary care center in Saudi Arabia,between 2018 and 2021. The association between BRCA positivity and proposed risk factors was evaluated using chi-square analysis. Multivariate analysis was performed using logistic regression to assess the association between independent significant risk factors and BRACA+. Results: 482 cases of breast cancer were reviewed, with 412 testing negative for mutations and an overall BRCA positivity rate of 13.7%. Among BRCA positive patients, 62% had a positive family history (p-value &amp;lt; 0.001), and they tended to be younger, with a median age of 38 compared to BRCA negative patients with a median age of 42 (p-value = 0.01). Of the 469 female patients, 62 (13%) were BRCA positive, and of the 12 male patients, 3 (25%) were BRCA positive. Among the BRCA positive patients, 73% had BRCA1 mutations, and 26% had BRCA2 mutations. No patients with lobular BC tested positive for BRCA mutations. The odds ratio for BRCA positivity in triple negative BC was 3.6 (95% CI 2.1-6.2, p-value &amp;lt; 0.001). The odds ratio for BRCA positivity in HR+ cases was 2.5 (95% CI 1.4-4.2, p-value = 0.001). In HR+ cases, 4.6% had BRCA1 mutations, and 5% had BRCA2 mutations. In ER- cases, 20% had BRCA1 mutations, and 1.2% had BRCA2 mutations. Multivariate analysis revealed that increasing the age of diagnosis by one year reduced the chance of having BRCA positivity by 5% (p-value = 0.009). Having a positive family history increased the risk of BRCA positivity with an OR of 8 (95% CI 4-15.8, p-value &amp;lt; 0.001), and triple negative BC increased the risk of BRCA positivity with an OR of 4.1 (CI 2.2-7.5, p-value &amp;lt; 0.001). The model performance was evaluated using an AUC of 0.80. Conclusion: This study highlights the high prevalence of BRCA mutations in a high-risk population of BC patients. The proposed predictive model identified younger age, triple negativity, and a positive family history as independent predictors, with an AUC of 0.8. The study's predictive model suggest that these factors may be useful in identifying patients who are at increased risk of carrying BRCA mutations and could benefit from genetic counseling and testing. Citation Format: Kausar Suleman, Khalid Al-Khatib, Emaan Haque, Tusneem El Hassan, Abdullah Al Suwaidan, Sabah Alaklabi, Taher Twegieri, Adhar AlSayed, Dahish Ajarim, Meshari Al Zahrani, Syed Saad Akhtar, Osama Al Malik, Amal Al Hefdhi, Wafa Khayal, Sitah Al Zughaibi, Asma Tulbah. Prevalence of BRCA Mutations: A Predictive Model in a High-Risk Population of BC Patients at a Tertiary Care Center [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 PO5-17-06.

Abstract PO5-05-14: Survival in Young Women with De Novo or Recurrent Metastatic Breast Cancer

Abstract Background. Approximately 12,000 women aged 40 years or younger are diagnosed with breast cancer every year in the United States alone. Limited data exist regarding survival in young women with metastatic breast cancer (MBC), particularly when considering modern tumor subtyping and treatment, though previous studies have suggested that patients presenting with MBC at diagnosis (de novo stage IV) have better prognosis than those who develop recurrent MBC after initial diagnosis of stage 0-III disease. We sought to determine survival rates in young patients with MBC stratified by disease presentation (de novo versus recurrent) and subtype. Methods. The Young Women’s Breast Cancer Study (YWS) is a multicenter, prospective cohort which enrolled 1,302 women diagnosed with stage 0-IV breast cancer at age ≤40 from 13 North American academic and community-based sites from 2006-2016. The current median follow-up is 10.1 (range 0.4-16.3) years. Histopathology slides were centrally reviewed for 97% of the participants, and clinical tumor molecular subtypes have been detailed. In the recurrent group, receptors were obtained from the initial breast surgery. Descriptive analyses were used to characterize patients with de novo or recurrent MBC, including demographic and disease characteristics, and survival rates. Overall survival was estimated using the Kaplan-Meier method and compared by log-rank test between those who presented with de novo and relapsed disease overall and within tumor subtypes. Results. Among 246 patients included in this analysis, 74.0% (n=182) had recurrent MBC and 26.0% (n=64) had de novo MBC. Most patients were white (n=208, 84.6%), while 6.9% were Asian (n=17), 4.5% Black (n=11), 0.8% Native American (n=2), 0.8% multiracial (n=2) and 2.4% other/unknown (n=6). A total of 4.5% of patients were Hispanic (n=11). Median age at diagnosis of de novo MBC was 37 years and 40 years for diagnosis of metastasis in the recurrent group. Median disease-free interval was 3.23 (range 0.32 – 13.84) years for the recurrent MBC group. Among all patients with MBC, most (55.7%, n=137) had estrogen receptor (ER) and/or progesterone receptor (PR)-positive, human epidermal growth factor receptor 2 (HER2)-negative disease, whereas 17.9% (n=44) had ER and/or PR-positive HER2-positive, 7.3% (n=18) had ER/PR-negative HER2-positive, and 18.7% (n=46) had triple-negative tumors. A greater proportion of participants (43.8%, n=28) had HER2-positive disease in the de novo group than in the recurrent group (18.7%, n=34), P=&amp;lt; 0.0001. A total of 10.9% (n=7) of de novo patients had a germline BRCA mutation, compared to 13.7% (n=25) in the recurrent group. Median survival was 5.09 (95% CI: 3.74 – 6.38) years in the de novo group and 2.63 (95% CI: 1.98 – 3.21) years in the recurrent MBC group (P=0.0004). When stratifying by subtype, survival among patients with de novo ER and/or PR-positive HER2-positive disease was longer than among patients with recurrent disease (P=0.0149), whereas there were no statistically significant differences in survival between the de novo and recurrent disease groups in other disease subtypes (Table 1). Conclusion. Survival in young women with MBC is highly heterogeneous and varies substantially by tumor subtype and disease presentation. Those with de novo ER and/or PR-positive HER2-positive subtype appear to have better outcomes than those with recurrent MBC with the same subtype. These findings can inform patient care and potential future research to improve outcomes for young patients with MBC. Table 1: Median survival by disease presentation and subtype * 1 patient with recurrent MBC was not included because the initial diagnosis was DCIS MBC: metastatic breast cancer; OS: overall survival; CI: confidence interval; ER: estrogen receptor; PR: progesterone receptor; HER2: human epidermal growth factor receptor 2 Citation Format: Leticia Varella, Yue Zheng, Shoshana Rosenberg, Gregory Kirkner, Craig Snow, Kathryn Ruddy, Rulla Tamimi, Jeffrey Peppercorn, Lidia Schapira, Virginia Borges, Steven Come, Laura Collins, Ellen Warner, Kate Dibble, Eric Winer, Ann Partridge. Survival in Young Women with De Novo or Recurrent Metastatic 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 PO5-05-14.

Abstract PS07-07: The RXR agonist, IRX4204, delays the formation of Brca1 mutant mammary tumors via modulation of the anti-tumor immune response

Abstract Background: Women with germline BRCA1 mutations are at an increased risk for developing breast cancer in their lifetime, often at a young age with more aggressive tumors. At present, prophylactic bilateral mastectomy is the most effective strategy for reducing breast cancer risk. However, this invasive procedure is irreversible and associated with potential complications. We and others have found that PARP inhibitors can delay Brca1-mutant tumor formation in mice and could be beneficial for the prevention of breast cancer. However, currently available PARP inhibitors are associated with modest toxicities that may not be acceptable to women without cancer. Thus, there remains an urgent need for the development of safe and effective therapies for the prevention of breast cancer. Here, we present data demonstrating the activity of IRX4204, a minimally toxic and highly specific agonist of the nuclear retinoid X receptor (RXR), to delay the formation of mammary tumors in a Brca1-deficient mouse model. This inhibitory effect on tumor growth is due, in part, to the role of IRX4204 in stimulating the anti-tumor immune response. Methods: We used the established MMTV-Cre, conditional Brca1 gene knockout, p53 heterozygous loss mouse model (BRCA1co/co; MMTV-Cre+/+; p53+/-) and selected for mutant female pups using PCR genotyping. At 16 weeks of age, all mice were separated into 4 treatment groups (n=10 per group): (1) sesame oil control; (2) the novel RXR agonist, IRX-4204 (10mg/kg); (3) high-dose IRX4204 (20 mg/kg); and (4) the RXR agonist, 9-cis-UAB-30 (5 mg/kg). All treatments were given by oral gavage five days per week, and mice were observed daily for tumor formation and toxicity. At the study endpoint, tumors and normal mammary glands were collected for additional analyses. Immunohistochemical staining was used to quantify CD8a, Ki-67 and cleaved caspase 3 expression in Brca1-deficient tumors. Oil Red O staining was used to measure changes in lipid accumulation in Brca1-deficient cell lines treated with IRX4204. qPCR was used to quantify the changes in gene expression of lipid metabolism-associated genes upon treatment with IRX4204 in vitro. Results: Vehicle-treated Brca1-deficient mice had a median time-to-tumor formation (TTF) of 211 days, with 100% developing tumors by 330 days. Mice treated with UAB 5 mg/kg had an improved median TTF of 261 days, whereas mice treated with IRX4204 10mg/kg or 20mg/kg had a median TTF of 347 and 304 days, respectively (p &amp;lt; 0.01). In addition, 60% of mice treated with IRX4204 10 mg/kg remained tumor-free at 330 days. IRX4204-treated tumors showed an increased infiltration of CD8-positive T-cells over vehicle-treated tumors (p &amp;lt; 0.05). Treatment of Brca1-deficient cell lines with IRX4204 in vitro resulted in a significant increase in lipid accumulation accompanied by a 2-fold increase of Srebf1 expression (a key transcription factor that regulates lipid homeostasis) within 24 hours of treatment (p &amp;lt; 0.05). Conclusion: These data demonstrate a novel use of the RXR agonist, IRX4204, to delay the formation of Brca1-deficient mammary tumors. We have found that IRX4204 treatment modulates the tumor immune response through increased infiltration of cytotoxic CD8-positive T-cells in Brca1-deficient mammary tumors in vivo. We have also determined that IRX4204 modulates lipid metabolism in breast cancer cell lines in vitro. It is known that lipid-derived antigens can stimulate T-cell activity. Our findings suggest that RXR agonists may alter lipid antigen production to activate an anti-tumor response. Additional immune and lipidomic studies are on-going. This work was supported by NCI-PREVENT grant (to PB and AM HHSN26100008) and CFP Foundation (Odyssey Fellowship to CM). Citation Format: Cassandra Moyer, Darian Coleman, Jamal Hill, Lana A. Vornik, Michelle Savage, Martin Sanders, Sei Shizuko, Altaf Mohammed, Powel Brown, Abhijit Mazumdar. The RXR agonist, IRX4204, delays the formation of Brca1 mutant mammary tumors via modulation of the anti-tumor immune response [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 PS07-07.

Abstract PO5-20-03: Phase I/II study of stereotactic radiosurgery with concurrent olaparib followed by adjuvant durvalumab and physician’s choice systemic therapy in subjects with breast cancer brain metastases

Abstract BACKGROUND: Despite progress in the treatment of brain metastasis for HER2+ breast cancer, outcomes for patients with HER2-negative breast cancer brain metastases remain poor. Current standard of care consists of local therapies, including surgery and radiotherapy, followed by systemic therapy. Preclinical studies show inhibitors of poly(ADP-ribose) polymerase (PARP) are effective in combination with radiation therapy as a DNA damage response inhibitor. Triple-negative breast cancer (TNBC) has higher rates of homologous recombination deficiency compared to other breast cancer subtypes, and together with HER2-negative, BRCA-mutated breast cancer would be particularly sensitive to PARP inhibition. PARP inhibition has also demonstrated promising efficacy combined with immunotherapy in patients with germline BRCA-mutant and metastatic TNBC in clinical trials (MEDIOLA, TOPACIO). In addition, immunotherapy with stereotactic radiosurgery (SRS) is associated with favorable intracranial control and survival in patients with brain metastases. We hypothesize that this biologically-driven combination will enhance local control of SRS-treated brain metastases through synergy with PARP inhibition, while controlling micrometastatic disease in the brain and extracranial sites via potentiation of the immune response. METHODS: We are conducting a multi-institution, Phase I/II trial of SRS plus olaparib, followed by durvalumab (with physician’s choice systemic therapy), for patients with TNBC (any BRCA status) or HER2-negative with BRCA-mutated (germline or somatic) breast cancer brain metastases [NCT04711824]. A total of 41 patients are planned for enrollment at 8 sites. The primary objectives are to evaluate safety and tolerability (Phase I) and determine intracranial disease control at 6 months (Phase II) of this treatment combination. Secondary objectives include determining clinical activity via intracranial and global progression-free survival, overall survival, and intracranial and extracranial response rate. Exploratory objectives will assess potential biomarkers of treatment response, including changes in circulating tumor cells and DNA in blood and cerebrospinal fluid, germline and tumor mutations in DNA repair pathway genes, and PD-L1 expression, as well as quality of life and patient-reported outcomes. A surgical sub-study (n=5) will evaluate olaparib concentration/distribution in resected brain metastases. As of June 2023, cohort 2 of phase I has been completed without dose-limiting toxicity. Citation Format: Colette Shen, Yara Abdou, Linda Chen, Xianming Tan, Gaorav Gupta, Mina Lobbous, Filipa Lynce, Erica Stringer-Reasor, Carey Anders. Phase I/II study of stereotactic radiosurgery with concurrent olaparib followed by adjuvant durvalumab and physician’s choice systemic therapy in subjects with breast cancer brain metastases [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 PO5-20-03.

Abstract PO3-24-06: Integrative genomic and CRISPR screen analysis identifies synthetic viability interactions in BRCA1/2 cancers

Abstract Background Pathogenic BRCA1 and BRCA2 (BRCA1/2) germline mutations contribute to hereditary breast cancer and are linked with increased risk of other cancers. Paradoxically, bi-allelic inactivation of BRCA1/2 (bBRCA1/2) is embryonically lethal. Although TP53 loss can at least in part mitigated the deleterious impact of Brca1 deficiency in mice, this is insufficient in human cells to compensate for decreased proliferative capacity. What other compensatory mechanisms facilitate oncogenesis remains unclear. Methods We performed an integrative analysis of cancer genomes from bBRCA1/2 tumors and CRISPR/Cas9 screens from cellular models to identify novel gene candidates that facilitate synthetic viability. First, we analyzed cancer genomes from ovarian and breast cancer derived from TCGA and identified genomic loci, which were enriched for recurrent copy number alterations (CNAs) in bBRCA1/2 tumors. We subsequently identified genes from these CNA loci that had corresponding changes in gene expression. Then, we used high-throughput genome-wide CRISPR/Cas9 knockout screens in BRCA1/2−/− cell lines (BRCA1−/- in RPE1 cells, BRCA2−/− in DLD1 cells) to identify which of these genes increased cell proliferation in vitro. Lastly, we experimentally validated these synthetic viable interactions using an orthogonal MCF12a system to evaluate changes in colony formation with a clonogenic cell survival assay. Results In human cancer genomes, we identified that bBRCA1/2 tumors harbored recurrent large-scale genetic deletions significantly more frequent than histologically matched control tumors. We identified 148 cytobands (23 distinct genomic loci) frequently deleted in bBRCA1/2 ovarian cancers (N=92), and 90 cytobands (15 distinct genomic loci) in bBRCA1/2 ER+ breast cancers (N=30). Subsequent computational analysis of gene expression data identified transcriptionally decreased genes in the frequently deleted loci. Cross-referencing with CRISPR/Cas9 screens in BRCA1/2−/− cells, we ultimately identified 277 and 218 genes that were altered in human tumors and putatively enhanced viability in BRCA1/2-null models but not in isogenic wild-type cell lines in BRCA1 and BRCA2 models, respectively. We subsequently selected 17 genes that either increased viability in BRCA1, BRCA2, or both contexts for experimental validation. Of these, about 40% (7 of 17) were experimentally validated (RIC8A, GNA12, ATMIN, IPO7, ATXN2, KDM1A, and NUP98) and had evidence of synthetic viability in this cellular context. Interestingly, RIC8A and GNA12 interact with each other, are both involved in G protein-coupled signaling pathway, and are synthetically viable with both BRCA1−/− and BRCA2−/− cells. In a re-analysis of a recently published genomic dataset on metastatic breast cancer, we found that homologous recombination deficient tumors developed additional loss of function mutations in RIC8A in the metastatic setting. Conclusions This study provides insights into the oncogenesis of BRCA1/2 malignancies and describes a high-throughput framework to identify synthetic viability interactions and causal driver genes affected by large-scale CNAs in human cancers. Citation Format: Yingjie Zhu, Xin Pei, Ardijana Novaj, Jeremy Setton, Fatemeh Derakhshan, Pier Selenica, Niamh McDermott, Sonali Sinha, Atif Khan, Simon Powell, Jorge Reis-Filho, Nadeem Riaz. Integrative genomic and CRISPR screen analysis identifies synthetic viability interactions in BRCA1/2 cancers [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 PO3-24-06.

Abstract PO3-14-11: Association between BRCA alterations detected by circulating tumor DNA and germline mutations in breast cancer patients: a retrospective mono-institutional analysis

Abstract Background: PARP inhibitors (PARPi) are a standard of care for breast cancer (BC) patients (pts) with germline BRCA (gBRCA) mutation, with benefit demonstrated also in patients with somatic (s) BRCA1/2 mutations. The use of circulating tumor (ct) DNA testing allows to detect resistant and actionable alterations in BC, but it could be associated with the incidental identification of germinal mutations. The aim of this study was to describe the incidence of both, somatic and germinal BRCA1/2 alterations, and the impact on the therapeutic outcomes in a retrospective BC cohort with clinical ctDNA testing for their BC. Materials and methods: A retrospective cohort of 245 BC pts that underwent ctDNA analysis (Guardant 360) between August 2014 and May 2023 at Weill Cornell Medical College was identified. Pts with at least a BRCA1/2 alteration, including variant of uncertain significant (VUS) and synonymous, were enrolled in the study. A descriptive analysis was performed. Results: Among 35 patients included, 34 had metastatic disease, the median age was 61 years old (IQR 40-67), and 65.7% were post-menopausal at diagnosis. 57.1% of pts had hormone receptor positive/HER2 negative (HR+/HER2-) BC, 20% had HER2 positive disease and 22.9% were triple-negative (TN) BC. Ten (28.6%) and 20 (57.1%) pts had a sBRCA1 or a sBRCA2 alteration on ctDNA, respectively; 5 pts (14.3%) had a coexisting sBRCA1/2 mutation. The median variant allele frequency (VAF) was 1.2% for BRCA1 and 2.7% for BRCA2 alterations. Furthermore, 53.3% and 6.7% of sBRCA1 and 40% and 8% of sBRCA2 mutations were identified as VUS and synonymous, respectively. The most common associated genomic alterations included TP53 (62.9%), ESR1 (20%) and PI3KCA (52%) with a median number of 4 variants (IQR 2-7). Next generation sequencing (NGS) testing on tissue was available for 3 patients: two demonstrated concordance with BRCA alterations detected by ctDNA, whereas no alteration in BRCA1/2 genes was found for the third patient despite the tissue analysis was performed at the same time of the ctDNA. Germline testing was available for 24 (69%) pts; a corresponding gBRCA1 mutation was found for 3 pts (VAF 48.6%-84.3%), and a gBRCA2 for 8 pts (VAF 26.7%-49.5%). Due to the small sample size, a univocal VAF cut-off to detect gBRCA1/2 mutations could not be calculated. Twenty-nine pts had a sBRCA1/2 mutation detected by ctDNA test before starting a new therapy; of these 55.2% had HR+/HER2- disease, while 17.2% and 27.6% were HER2 positive and TN BC, respectively. The median progression free survival (mPFS) was 10.3 (3.2-17.4) months (ms) and the 1-year and 2-year overall survival (OS) rates were 82.3% and 70.5%, respectively. The mPFS was 10.3 ms (0-25.0) for patients (n=16) that underwent chemotherapy, 5.6 ms (0-15.1) for those who had received endocrine therapy (n=9), and not reached for patients treated with PARPi (n=4). Conclusions: ctDNA analysis allows the detection of sBRCA1/2 mutations that could be missed by tissue-based testing. The identification of BRCA alterations on ctDNA could guide the use of germline testing even when these are present at a lower VAF than expected, with relevant impact on the therapeutic choices and family screening. Further evaluation to establish the impact of sBRCA1/2 detected by ctDNA on the therapeutic algorithm decision are needed. Citation Format: Letizia Pontolillo, Eleonora Nicolò, Laura Munoz Arcos, Carolina Reduzzi, Mara Serena Serafini, Amanda Kaylan Strickland, Nadia Bayou, Jeannine Donahue, Elisabetta Molteni, Lorenzo Gerratana, Diana Giannarelli, Eleni Andreopoulou, Emilio Bria, Massimo Cristofanilli. Association between BRCA alterations detected by circulating tumor DNA and germline mutations in breast cancer patients: a retrospective mono-institutional analysis [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 PO3-14-11.

Abstract PO3-17-10: Real-World evidence for Pembrolizumab-based neoadjuvant chemotherapy in early-stage triple negative breast cancer: a single institution experience

Abstract Introduction The improved pathologic complete response (pCR) and event-free survival observed in Keynote-522 trial (NCT03036488) led to the adoption of (neo)adjuvant pembrolizumab (pembro)-based chemotherapy (CT) for high-risk early-stage triple-negative breast cancer (eTNBC) in various jurisdictions. However, Real-World Evidence (RWE) for (neo)adjuvant pembro in this setting would further support its ongoing funding and utilization. The aim of this study was to provide RWE for (neo)adjuvant pembro in eTNBC in the United Arab Emirates (UAE), where patients often present with more-advanced disease stages and poorer prognostic profiles compared with North America and Europe. Method This is a retrospective cohort study involving all patients treated with pembro-based neoadjuvant chemotherapy (NACT) for eTNBC at a major cancer center (Tawam Hospital) in the UAE between October 2021 and June 2023. Patient characteristics, clinicopathologic features, immune related adverse events (irAE) and disease outcomes were reported by descriptive statistics. An exploratory analysis was also conducted to examine the associations between pCR and HER-2 status (HER2 negative vs HER2 low) as well pCR and treatment interruption (&amp;lt; vs = &amp;gt; 2 weeks). ResultA total of 41 patients, with a median age of 44 years, were included in this study. All had an ECOG status of 0-1. The clinical and pathological characteristics are provided in Table 1. Pathogenic germline BRCA (gBRCA) mutations were detected in 8 (21%) of the 38 patients who underwent testing, including 6 with gBRCA1 and 2 with gBRCA2), with additional TP53 and SMARC4 detected in one patient each. Approximately 66% of the patients (n = 27) completed surgery post neoadjuvant pembro+CT, of whom 18 (67%) had breast conserving surgery and 9 (33%) had mastectomy. Of the patients who underwent surgery, 60% (n = 16/27) achieved pCR including 68% (13/19) of the IHC 0+ and 37.5% (3/8) of the HER2 1+ or 2+ ISH negative (p-value = 0.429, Chi Square test). Of the total population, 16 (40%) did not complete NACT; 1 lost to follow-up, 9 were still on ongoing therapy, 2 discontinued therapy due to toxicity, and 4 developed progressions including 1 locoregional relapse, and 3 metastatic diseases. Of the 32 patients who completed at least 3 months of pembro-NACT, 14 (34%) reported any grade irAE: skin toxicity (N = 3, 21%), hypothyroidism (N = 8, 57%), Hyperthyroidism (N = 1, 7%), Hepatitis (N = 4, 28.5%), adrenal insufficiency (N = 1, 7%), and pneumonitis (N = 1, 7%). With a median follow up of 4.5 months, pembro was postponed in 4 patients and permanently discontinued in 1 secondary to severe pneumonitis requiring ICU admission. All irARs were graded at I and II, except for 1 grade III dermatitis, and 1 grade III pneumonitis. Interruption of IO was required for irAE in 5 (36%) patients, and steroids were administered in 4 (29%). pCR was observed in 6 (40%) patients out of 15 who experienced treatment interruption due to IrAE or CT and 10 out of 13 (77%) in those who did not experience treatment interruption (p = 0.04895, Chi-square test). Conclusion The pCR rates for Pembro-based NACT in this RWE study, involving patients with an overall higher risk disease, appeared to be consistent with those observed in keynote-522. Interestingly, pCR rates did not seem to differ between HER2 negative and HER2 low groups. However, pCR rates appeared to be lower in patients who experienced treatment interruptions. Approximately half of the patients developed irAE but the majority of the adverse events were of lower grade and did not require treatment interruptions. Overall, the RWE observed in this study supports the ongoing funding and utilization of Pembro-based NACT in eTNBC. Updated data, including the pCR rate and toxicity, will be presented at the meeting once most of the patients have completed surgery. Table 1: Clinical and Pathological Characteristics of patients (Nf41) XX- XX Citation Format: Aydah Al-Awadhi, Mouza AlShebli, Lina Wahba, Tallal Younis. Real-World evidence for Pembrolizumab-based neoadjuvant chemotherapy in early-stage triple negative breast cancer: a single institution experience [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 PO3-17-10.

Abstract PS07-09: Prenatal BRCA1 epimutations is a major cause of triple-negative breast cancer

Abstract Background: Low level normal cell BRCA1 epimutations have been associated with an increased risk of triple-negative breast cancer (TNBC). However, the fraction of TNBCs that may have BRCA1 epimutations as their underlying cause is unknown. Neither are the time of occurrence and the potential inheritance pattern of BRCA1 epimutations established. Methods: To address these questions, we analyzed BRCA1 methylation status in breast cancer tissue and matched white blood cells (WBC) from 411 patients with primary breast cancer, including 66 TNBCs. Samples were analyzed by a highly sensitive next-generation sequencing (NGS) assay on an Illumina MiSeq sequencer, allowing allele-resolved methylation assessment. Further, to assess the time of origin and the characteristics of normal cell BRCA1 methylation, we analyzed umbilical cord samples from 1260 newborn girls and 200 newborn boys.To assess potential Mendelian heritage, we analyzed BRCA1 methylation status in WBCs from 575 mothers and 531 fathers of newborn girls with (n = 102) and without (n = 473) WBC BRCA1 methylation. Results: We found concordant tumor and mosaic WBC BRCA1 epimutations in 10 out of 66 patients with TNBC and in four out of six patients with estrogen receptor (ER)-low expression (&amp;lt; 10%) of tumors (combined 14 out of 72; 19.4%, CI: 11.1-30.5). These exceeded the number of tumors harboring germline (n = 5) or somatic (n = 4) BRCA1 mutations. Notably, BRCA1 methylation and BRCA1 mutations were mutually exclusive. Contrasting the findings in TNBC and ER-low exprssion tumors, we found WBC and tumor BRCA1 methylation concordance in only three out of 221 patients with ER &amp;gt;10+% tumors and zero out of 116 patients with HER2 positive tumors. Intraindividually, BRCA1 epimutations affected the same allele in normal and tumor cells. Assessing BRCA1 methylation in umbilical cord WBCs from newborn girls, we found mosaic, predominantly monoallelic BRCA1 epimutations, with qualitative features similar to those in adults, in 113/1260 (9.0%) of individuals. We found no correlation between WBC BRCA1 methylation in newborns and methylation status in their mothers, fathers, or any parent. Notably, WBC BRCA1 methylation occurred at a significantly lower frequency in newborn boys ( 9/200; 4.5%) as compared to newborn girls (p = 0.038). Similarly, WBC BRCA1 methylation was found less common among fathers (16/531; 3.0%), as compared to mothers (46/575; 8.0%; p = 0.0003). Conclusions: Our findings suggest prenatal BRCA1 epimutations might be the underlying cause of around 20% of TNBC and low-ER expressing breast cancers. Such constitutional mosaic BRCA1 methylation likely arise through gender-related mechanisms in utero, independent of Mendelian inheritance. Citation Format: Per Lonning, Hans Petter Eikesdal, Elisabet Ognedal, Bjornar Gilje, Steinar Lundgren, Egil Blix, Helge Espelid, Jürgen Geisler, Stephanie Geisler, Emiel Janssen, Synnøve Yndestad, Laura Minsaas, Beryl Leirvaag, Reidun Lillestol, Stian Knappskog, Oleksii Nikolaienko. Prenatal BRCA1 epimutations is a major cause of 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 PS07-09.

Abstract PO3-03-04: Metaplastic breast cancer: a single center retrospective study

Abstract Background: Metaplastic breast cancer (MBC) is a rare malignancy that accounts for up to 1% of all primary invasive breast carcinomas (BC). It is histologically heterogeneous, usually presents with a triple-negative phenotype and comprises low-grade and high-grade (HG) variants. HG variants have a higher risk of recurrence and a shorter disease-free and overall survival compared to other BC subtypes. Our research aimed to estimate the prevalence of HG-MBC among the Slovenian population and determine the characteristics of patients (pts) and tumours and the disease outcome. Patients and methods: Our retrospective study included pts diagnosed with HG-MBC at the Institute of Oncology Ljubljana from January 1983 until January 2021. Clinicopathologic characteristics such as tumour subtype, size and grade, nodal status, hormonal receptors (HR) and HER-2 status, lymphovascular invasion (LVI), tumour-infiltrating lymphocytes (TIL) and presence of germline BRCA mutation status were determined. The survival analyses were performed using the Kaplan-Meier method. The Cox proportional hazard model examined the association between risk factors and survival outcomes. Results: We evaluated 113 HG-MBC pts among a total of 27700 pts diagnosed with BC over 38 years (0.41%). The median age was 61.6 years (range 29.7 -93.9), majority of pts were postmenopausal (78.69%). The median follow-up was 15.5 years. The most common tumour subtype in our cohort was mixed MBC (53 cases, 46.9%), followed by MBC with mesenchymal differentiation (24 cases, 21.2%), squamous cell carcinoma (20 cases, 17.7%) and spindle cell carcinoma (16 cases, 14.2%). From the 113 evaluated pts, we obtained data about the stage in 105 pts, pathological tumour size in 100 pts, number of positive lymph nodes in 99 pts, HR status in 95 pts, HER2 status in 76 pts, grade in 97 pts, LVI in 85 pts, MIB-1 in 41 pts and TIL in 77 pts. At diagnosis, 17/105 pts (16.2%) had stage I disease, 59/105 pts (56.2%) stage II, 25/105 pts (23.8%) stage III and 4/105 pts (3,8%) stage IV. Most tumours were poorly differentiated (90/97, 92.2%) without LVI (60/85, 70.6%). Only 6/95 (6,3%) pts had positive HR, 7/76 (9.2%) pts had positive HER-2 status and 8/77(10.4%) pts intensive TIL. Overall, 13 pts were tested for BRCA germline mutation, among which only 1 (7,7%) had BRCA1 mutation. Modified radical mastectomy was the most frequent type of surgery (63.5%); 49.5% of the patients received radiotherapy. In total, 66/113 pts received CT: from 1983 to 2000, 16/36 (44.4%), and after 2000 50/77 (74.9%). In the first period, most pts received CMF (14/16; 87.5%) and anthracyclines and taxanes (27/50; 54%) in the second period. The disease progressed at 37 pts. At 19 pts, new malignancies were found. 55 pts died, 37 of them because of BC. Five- and 10-year disease-free survival (DFS) was 61.7% and 54.1%, while 5-and 10-year overall survival (OS) was 67.1 % and 56.7%, respectively. However, DFS and OS did not differ between the pre-2000 and post-2000 periods. The best outcome was found in pts with squamous cell carcinoma (5- and 10-year DFS 83.5% and 77.0% and 5-and 10- year OS 89.4 % and 83.0%). A subtype of MBC (squamous cell vs other) was the only predictive factor in multivariate analysis for both DFS (HR 0.21; 95% CI 0.05-0.92; p = 0.038 and OS (HR 0.27; 95%CI 0.09-0.78; p = 0.016), no association was seen between survival and tumour size, nodal status, stage, HR and HER2 status, grade, LVI and TILs. Visceral organs were the most common localization of distant metastases (21/37, 56.8%). Metastases in CNS occurred in 9/37 (24.3%) pts. Median OS after the first progression was only 0.9 years. Conclusions: The proportion of HG-MBC in our cohort of pts is 0.41%. Disease outcomes are poor; the 10-year OS of pts with early HG-MBC is only 56.6% and has not improved during the last decades. Squamous cell differentiation predicts a better outcome and is the only independent predictive factor of DFS and OS among HG-MBC pts. Citation Format: Maša Auprih, Gorana Gasljevic, Eva Setina, Anja Zizek, Simona Borstnar. Metaplastic breast cancer: a single center retrospective study [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 PO3-03-04.

Abstract PO2-05-14: Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort

Abstract Background: HER2-negative breast cancers expressing low (1-9 %) immunohistochemistry levels of hormone receptors (HR, estrogen and progesterone receptors), remain an uncertain category, being considered either as triple negative breast cancers (TNBC) or HR-positive (HR+) tumors across guidelines or approvals. The issues regarding this clinical subgroup are both prognostic, with the need of a better definition of their clinical outcome, as well as predictive. Methods: The ESME database is a French National cohort of all consecutive patients who initiated a first-line treatment for metastatic breast cancer (MBC) from 2008 on, in one of the 18 French Comprehensive Cancer Centers. Patients with HER2-negative (0 to 2+, ISH negative) MBC and known estrogen receptor (ER) and progesterone receptors (PR) expression levels were selected. Primary objective was to evaluate crude overall survival (OS) in HER2-/HR-low (ER and PR 0-9 and not TNBC) MBC pts compared with those with TNBC and HR+ disease defined by ER and PR &amp;lt; 1%, and ER ± PR ≥ 10%, respectively. In these 3 populations, predefined secondary objectives were to evaluate PFS under first line chemotherapy (CT), to describe clinical characteristics and the distribution of genetic abnormalities identified at the time of MBC diagnosis. Results: Out of 30,459 patients in the ESME database initiating their MBC treatment between 01/2008 and 01/2021, 19109 patients (2113 TNBC; 228 HR-low; 16768 HR+) were eligible for this analysis. Median follow-up was 58.0 months (95%CI [56.6; 59.0]). Median OS were 15.7 months [15.0-16.8], 19.1 months [15.5-22.4] and 44.6 months [43.8-45.5] in the TNBC, HR-low and HR+ subgroups, respectively. The multivariable analysis adjusted on age at MBC diagnosis, pathological grade and subtype, metastatic-free interval, number and sites of metastases and HER2 status (0 vs. 1-2+), identified no significant OS difference between HR-low and TNBC subgroups (HR=0.95, 95%CI 0.79-1.14), while HR+ patients had a better OS than TNBC patients (reference) (HR=0.50, 95%CI 0.47-0.53). Of these 19109 pts, 8910 received first-line CT regimen (1960 TNBC; 195 HR-low; 6755 HR+): taxanes-based: 66.7%, anthracyclines-based: 32.9%, capecitabine: 18%. Median PFS under first line CT were 5.3 (5.1-5.6), 5.1 (4.1-6.2) and 10.2 months (9.9-10.6) for TNBC, HR-low and HR+ subgroups, respectively. In the multivariable analysis adjusted on the same variables, the HR-low subgroup had a statistically poorer PFS compared to TNBC (HR=1.24, 95% CI 1.04-1.49). On the other hand, the HR+ subgroup had a better PFS than the TNBC (HR=0.74, 95%CI [0.70; 0.78]). Baseline germline BRCA1 mutations (at MBC diagnosis) were present in 4.5% of the TNBC cases, 2.6% of the HR-low cases, and 0.4% of the HR+ cases. The distribution of germline BRCA2 mutations was more homogeneous between the three groups (0.9% of TNBC cases, 1.3% of HR-low cases and 1.1 % of HR+ cases). Conclusions: In this large cohort, patients with HER2-negative, HR-low MBC seem to share similar general prognosis, oncogenetic features and PFS under standard chemotherapy treatment with TNBC patients. Citation Format: Marie Alexandre, Ludovic Gauthier, Audrey Mailliez, Thibault DE LA MOTTE ROUGE, Thomas Bachelot, Monica Arnedos, Florence Dalenc, Etienne Brain, Jean-Marc Ferrero, Vincent Massard, Isabelle Desmoulins, Marie-Ange Mouret-Reynier, Christelle Levy, Anthony Gonçalves, Marianne Leheurteur, Thierry Petit, Jean-Sébastien Frenel, Lise Bosquet, Suzette Delaloge, William Jacot. Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort [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 PO2-05-14.

Abstract PO3-08-04: Prevalence of BRCA1/2 mutations in an underrepresented population of women with breast cancer: Observations from the City of Hope INSPIRE study

Abstract Background: Because African American and Latina women have been less likely to undergo germline testing, it has been difficult to determine the prevalence of hereditary breast and ovarian cancer predisposition in these populations. Here we report the prevalence of BRCA1/2 mutation in patients with a breast cancer diagnosis from City of Hope’s (COH) INSPIRE (Implementing Next-generation Sequencing for Precision Intervention and Risk Evaluation) study. Methods: Patients with a history of any stage breast cancer (stage 0-IV), who were seen by a City of Hope physician at the Duarte or Upland campuses, were approached by a clinical research coordinator for participation in an institutional tissue biorepository project. Demographic information included age, race and ethnicity. Patients consent for this IRB-approved study to store tumor specimens for future research use and Invitae germline testing for 155 predisposition genes which is performed at no cost to the patient. Results: From 7/9/20 until 4/2023, 2413 women consented for participation and underwent germline testing. Mutations in BRCA1 were identified in 53 and BRCA2 in 65. Table 1 summarizes the prevalence of BRCA1/2 mutations according to race and ethnicity. Pathogenic variants in BRCA1 were identified in 22/742 (3.0%) of Hispanic women compared to 16/1552 (1.7%) non-Hispanics (p=0.046). BRCA2 mutations were comparable 16/742 (2.2%) Hispanics and 47/1505 (3%) non-Hispanics. Hispanic women with breast cancer were 2.49 times as likely as non-Hispanics to carry a pathogenic germline BRCA1 mutations than BRCA2 (p=0.026) Conclusion: The prevalence of BRCA1/2 mutations in the African American and Latina population is higher than what was observed in White women. These data provide additional support for the recommendation to perform germline testing in all women with breast cancer, regardless of race or ethnicity Prevalence of BRCA 1 and 2 mutations by Self-Reported Race and Ethnicity # Tested BRCA1 BRCA2 BRCA1 or 2 VUS/Negative Race Native American 15 0 1 (6.7%) 1 (6.7%) 14 (93.3%) Pacific Islander 8 0 0 0 8 (100%) Asian 367 5 (1.4%) 11 (3%) 16 (4.4%) 351 (95.6%) Black 136 7 (5.1%) 4 (2.9%) 11 (8.1%) 125 (91.9%) White 1675 37 (2.2%) 44 (2.6%) 81 (4.8%) 1594 (95.2%) Other 86 1 (1.2%) 4 (4.7%) 4* (4.7%) 82 (95.3%) Unknown 126 3 (2.4%) 1 (0.8%) 5 (3.2% 122 (96.8%) TOTAL 2413 53 (2.2%) 65 (2.7%) 117 (4.8%) 2296 (95.2%) Ethnicity Hispanic 742 22(3%) 16 (2.2%) 37* (5%) 705(95%) Non-Hispanic 1552 26(1.7%) 47(3%) 73(4.7%) 1479 (95.3%) Unknown 119 53(2.2%) 2(1.7%) 7(5.9%) 112(94.1%) TOTAL 2413 53(2.2%) 65(2.7%) 7(5.9%) 112(94.2%) * Patient had both BRCA1 and BRCA2 mutations Citation Format: Joanne Mortimer, Sydney Lindsey, Ilana Solomon, Wai Park, Duveen Sturgeon, Kathleen Blazer, Stacy Gray, Joseph Bonner, Xiaoyu Xia, Stephen Gruber. Prevalence of BRCA1/2 mutations in an underrepresented population of women with breast cancer: Observations from the City of Hope INSPIRE study [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 PO3-08-04.

Abstract PO1-13-05: Genomic characteristics and its therapeutic implications in breast cancer patients with detectable molecular residual disease

Abstract Background: Breast cancer constitutes approximately 30% of cancers in women, with a mortality-to-incidence ratio of 15%. While early and middle-stage breast cancer patients can undergo radical surgical resection, postoperative recurrence remains a significant challenge for clinicians. Molecular residual disease (MRD) is the main cause of postoperative recurrence of breast cancer. However, the baseline tumor genomic characteristics and therapeutic implications of breast cancer patients with detectable MRD are still unknown. Methods: In this study, we enrolled 80 patients with breast cancer who underwent next-generation sequencing (NGS)-based genetic testing of 1,021 cancer-related genes performed on baseline tumor and postoperative plasma from Army Specialty Medical Center between June 2017 and January 2023. The criteria for the patient’s enrollment were: (1) pathological diagnosis as breast cancer, (2) no distal metastasis, (3) radical surgery and R0 resection, (4) 1021 cancer-related gene testing of the tumor, (5) plasma MRD testing performed within 3 months after surgery and before adjuvant therapy. Results: A total of 18 patients in our cohort had detectable MRD. Baseline clinical characteristics found that patients with higher clinical stages were more likely to have detectable MRD. Analysis of single nucleotide variations and small insertions/deletions in baseline tumors showed that somatic mutations in MAP3K1, ATM, FLT1, GNAS, POLD1, SPEN, and WWP2 were significantly enriched in patients with postoperative MRD. Oncogenic signaling pathway analysis revealed that alteration of the Cell cycle pathway was more likely to occur in patients with detectable MRD (p=0.0125). Mutational signature analysis showed that defective DNA mismatch repair and activation-induced cytidine deaminase (AID) mediated somatic hypermutation (SHM) were associated with detectable MRD. Somatic copy number variation analysis found that amplification of CDKN2A, HOXB13, PPM1D, MPL, and VHL was significantly enriched in patients with detectable MRD. According to the OncoKB database, 77.8% (14/18) of patients with detectable MRD had U.S. Food and Drug Administration-approved mutational biomarkers and targeted therapy. Conclusion: For the first time, our study reports genomic characteristics of breast cancer patients with detectable MRD. The tumor biology is probably the main driver of detectable MRD. We also found the vast majority of patients with detectable MRD have the opportunity to access targeted therapy. Keywords: Breast cancer, MRD, Genomic character, Cell cycle pathway, Defective DNA mismatch repair, Activation-induced cytidine deaminase Figure 1. Somatic mutational landscape and clinical actionability of breast cancer patients with detectable MRD A. Oncoplot of top 20 genes altered in patients with detectable MRD. B. Forest plot of different mutant genes between patients with detectable and undetectable MRD. OR means odds ratio. Inf means infinity. ＊ means P-value &amp;lt; 0.05. C. The ten cancer-related signaling pathways were affected by somatic mutations both in patients with detectable and undetectable MRD. ＊ means P-value &amp;lt; 0.05. D&amp;E. The fraction and etiology of each signature in patients with detectable (D) or undetectable (E) MRD. F. The number of patients with detectable MRD in different actionable alterations. gBRCA1 means germline BRCA1 mutation. sBRCA1 means somatic BRCA1 mutation. sBRCA2 means somatic BRCA2 mutation. TMB-H means TMB-High. Citation Format: Xu Yan, Shu Zhang, Lu zhou, Yan Jiang, Jing Xu, Gang Zhang, Lu Shen. Genomic characteristics and its therapeutic implications in breast cancer patients with detectable molecular residual disease [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 PO1-13-05.