Prevalence of mutations in BRCA and homologous recombination repair genes and real-world standard of care of Asian patients with HER2-negative metastatic breast cancer starting first-line systemic cytotoxic chemotherapy: subgroup analysis of the global BREAKOUT study

Background The multinational BREAKOUT study (NCT03078036) sought to determine the prevalence of germline BRCA1/2 (gBRCA1/2) and somatic BRCA1/2 (sBRCA1/2) mutations and mutations in other homologous recombination repair (HRR) genes in women with HER2-negative metastatic breast cancer (MBC) starting first-line chemotherapy. Methods Genetic testing for gBRCA, sBRCA, and HRR gene mutations was performed in patients who started first-line chemotherapy for MBC in the last 90 days (341 patients across 14 countries) who were not selected based on risk factors for gBRCA mutations. We report data from the Asian cohort, which included patients in Japan (7 sites), South Korea (10 sites), and Taiwan (8 sites). Results Of 116 patients screened, 104 patients were enrolled in the Asian cohort. The median age was 53.0 (range 25–87) years. gBRCA1/2, gBRCA1, and gBRCA2 mutations were detected in 10.6% (11/104), 5.8% (6/104), and 4.8% (5/104) of patients, respectively; none had mutations in both gBRCA1 and gBRCA2. gBRCA1/2 mutations were detected in 10.0% (6/60) and 11.6% (5/43) of patients with hormone receptor-positive and triple-negative MBC, respectively. HRR gene mutations were tested in 48 patients without gBRCA mutations, and 5 (10.4%) had at least one HRR mutation in sBRCA, ATM, PALB2, and CHEK2. Conclusion We report for the first time the prevalence of gBRCA and HRR mutations in an Asian cohort of patients with HER2-negative MBC. Our results suggest that BRCA mutation testing is valuable to determine appropriate treatment options for patients with hormone receptor-positive or triple-negative MBC. Study registration NCT03078036.