Patterns of Homologous Repair Deficiency and <i>BRCA1</i> / <i>2</i> Testing of Ovarian and Breast Cancers: A Real-World Study of Patients in Community Health Settings in the United States

PURPOSE Testing to measure homologous repair deficiency (HRD) in certain cancers can identify patients who may benefit from poly(ADP-ribose) polymerase inhibitors. We examined real-world patterns and factors associated with testing to measure HRD (eg, BRCA1 / 2 , loss of heterozygosity, and genomic instability) in epithelial ovarian cancer (EOC) and BRCA1 / 2 mutations in human epidermal growth factor receptor 2–negative metastatic breast cancer (mBC) and their prevalence. METHODS We described demographic and clinical characteristics of patients diagnosed with EOC or mBC between 2018 and 2020 in a community health setting, by testing, and HRD (EOC cohort) or BRCA1 / 2 (mBC cohort) status. Logistic regression models were used to identify factors associated with testing and positivity. RESULTS In both cohorts, patients were older and predominantly White non-Hispanic and had advanced-stage disease at initial diagnosis. A total of 75% (748 of 1,002) and 46% (462 of 1,002) of the EOC and mBC cohorts were tested; testing and positivity were more common in younger patients. Testing was relatively more common among patients with EOC with high-grade serous and endometrioid tumors and less common among non-White patients and patients with less favorable performance status. Testing was relatively more common among patients with mBC with triple-negative breast cancers (TNBCs) and less common among patients with de novo mBC. Among genetic counseling recipients, 32% (174 of 547) of patients with EOC and 13% (38 of 282) of patients with mBC received counseling from a health care professional other than a genetic counselor. HRD and BRCA1 / 2 positivity was 29% and 11% in the EOC and mBC cohorts, respectively. Positivity was relatively more common among non-White non-Hispanic patients with EOC and patients with high-grade serous or endometrioid tumors. Positivity was relatively more common among patients with TNBC. No additional factors were associated with positivity in regression models. CONCLUSION Efforts should be made to increase testing among likely HRD- or BRCA1 / 2 -positive patients for whom targeted treatment options are available.