Luo, Linlin

PURPOSE Testing for germline BRCA1 and/or BRCA2 mutations (gBRCAm) is recommended for patients with human epidermal growth factor receptor 2–negative (HER2–) breast cancer (BC) to guide treatment selection with poly (ADP-ribose) polymerase inhibitors (PARPis). However, real-world data on germline BRCA1 and/or BRCA2 (gBRCA) testing and PARPi treatment patterns in metastatic BC (mBC) are limited. METHODS Deidentified patient data from adults diagnosed with HER2– mBC between 2014 and 2022 were captured from electronic health records in the US Flatiron Health database. gBRCA testing patterns and prevalence were examined by tumor subtype (hormone receptor–positive [HR+]/triple-negative) and disease stage at diagnosis. Demographic and clinical characteristics were described by receipt of gBRCA testing and PARPi. PARPi treatment patterns were assessed, and real-word overall survival (OS) was estimated in patients with gBRCAm diagnosed with mBC after January 1, 2018. RESULTS Of the 15,006 total patients, 4,654 (31.0%) received a gBRCA test. gBRCA testing rates mostly increased from 2014 to 2022 and were lower in patients with HR+ than triple-negative tumors. Of the patients who underwent gBRCA testing, 337 (7.2%) had gBRCAm. From 2018 to 2022, PARPi was initiated in 94 (45.6%) of 206 patients with gBRCAm. With a median follow-up of 22.8 months across patients with available first-line treatment start dates, real-world OS was numerically longer among 94 patients with gBRCAm who received PARPi (32.3 months [95% CI, 22.7 to 47.4]) than among 99 patients who did not (21.9 months [95% CI, 18.4 to not reached]). CONCLUSION Although gBRCA testing increased over time, testing and PARPi utilization rates remained suboptimal in potentially eligible patients with HER2– mBC. Exploratory analysis showed numerically longer OS in patients who received PARPi. Wider and timelier gBRCA testing is warranted to inform potentially optimal treatment decisions.

1113 Background: Testing for BRCA1/BRCA2 mutations (BRCAm) aids systemic treatment decisions for patients (pts) with metastatic breast cancer (mBC). This retrospective study explored real-world germline/tumor (g/t) BRCA testing patterns and PARP inhibitor (PARPi) use in US pts with mBC. Methods: Data from pts ≥18 years old diagnosed with HER2-negative mBC from 2014–2022 were captured in the nationwide Flatiron Health electronic health record-derived deidentified database. Patterns and timing of prospective or incidental BRCA testing were compared across mBC subtypes (hormone receptor-positive [HR+ mBC]/triple-negative mBC [mTNBC]) and disease stage (recurrent/ de novo). BRCAm prevalence was compared by testing modality and mBC subtype. PARPi initiation was assessed in pts with mBC diagnosed from 2018 onwards and a positive BRCAm test result. Clinical characteristics were compared by receipt of a BRCA test, testing modality, and PARPi initiation. Real-world overall survival (OS) by PARPi use was estimated using the Kaplan-Meier method. Results: Of 15,006 pts (including 12,349 with HR+ mBC; 1998 with mTNBC), 8178 (54.5%) did not receive any type of BRCA test, 4654 (31.0%) received a gBRCA test, 3075 (20.5%) received a tumor tissue DNA (ttDNA) test, and 1418 (9.4%) received a circulating tumor DNA (ctDNA) test. BRCA testing prevalence was numerically higher in pts with mTNBC (n=1164; 58.3%) than in pts with HR+ mBC (n=5323; 43.1%). As expected, testing prevalence was higher with ttDNA than with ctDNA (mTNBC: n=569 [28.5%] vs n=137 [6.9%]; HR+ mBC: n=2339 [18.9%] vs n=1224 [9.9%]). Over 93% of pts (recurrent and de novo) who received a tBRCA test were tested after an mBC diagnosis, and >1/3 were tested after first-line therapy, with median times from diagnosis to a ttDNA and ctDNA test of 127 and 431 days, respectively. Both gBRCA and tBRCA testing rates increased from 2014–2022, and testing occurred earlier in pts with recurrent than de novo disease. Among pts with tBRCAm, 66.0% had HR+ mBC, and 25.6% had mTNBC. BRCA1 mutations were more common in mTNBC (59.0%) than in HR+ mBC (22.9%) tumors. Of 219 pts with tBRCAm tumors who were diagnosed with mBC from 2018 onwards, PARPi was initiated in 39/74 (52.7%) pts with gBRCAm, 15/71 (21.1%) pts who were gBRCAm-negative, and 19/74 (25.7%) pts with gBRCAm status unknown. Among pts with g or tBRCAm and available OS data, median OS was numerically longer in pts who received PARPi (32.3 months [95% CI: 24.2, 47.4], n=128) versus pts who did not (29.0 months [95% CI: 21.9, 31.9], n=204; median follow-up time 23.2 months). Conclusions: While NCCN guidelines recommend gBRCA testing for all pts with mBC, more than half of pts with HER2-negative mBC (56.9% of pts with HR+ mBC) did not receive any BRCA test. Among pts with tBRCAm, ~2/3 had HR+ disease. Despite the potential benefits of PARPi for pts with BRCAm mBC, utilization remained low from 2018–2022.

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; < 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 ( > 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, < 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 & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, US Legal entity responsible for the study: AstraZeneca. Funding: This study was supported by AstraZeneca and Merck Sharp & Dohme LLC, a subsidiary of Merck & 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.