Abstract P5-03-14: Prevalence of germline BRCA mutations in unselected Korean patients with HER2-negative breast cancer: A Prospective cohort study

Abstract Backgrounds Since OlympiAD study, National Comprehensive Cancer Network guideline recommends assessment of germline BRCA1/2 mutation in all patients with recurrent or metastatic breast cancer to identify candidates for PARP inhibitor therapy, which is not always possible in clinical practice due to limited resources for testing. Data on the prevalence of gBRCA mutation is still lacking, especially in patients with non-high risk for hereditary breast and ovarian cancer syndrome. In this study, we investigated prevalence of gBRCA mutation in unselected Korean patients with HER2-negative advanced BC in a prospective cohort and analyzed oncologic outcome. Methods Eligible patients were diagnosed with HER2-negative advanced BC and had initiated palliative systemic treatment. Peripheral blood was prospectively drawn from each patient and gBRCA mutation status was assessed by next generation sequencing using NGeneBio BRCAaccuTest®. In 100 patients, somatic mutations including BRCA1/2 from tumor tissue were investigated using targeted panel sequencing. To estimate the prevalence of gBRCA mutation with margin of error to be no more than ±4% at the 95% confidence interval in a population size of 20,000, 583 patients were to be enrolled. Results A total of 583 patients were enrolled between Oct 2019 and Mar 2022, and the prevalence of gBRCA mutation was analyzed in 570 patients, excluding ineligible patients. Median age was 54 years old (range 26-87) and 567 patients were female. 475 patients had HR+/HER2- BC and 94 patients had triple negative breast cancer (TNBC). The overall prevalence of gBRCA1/2 pathogenic mutation was 7.3% (42/570) in unselected patients. The prevalence of gBRCA1 mutation was 1.6%(9/570) overall, 0.8%(4/475) in HR+/HER2- BC, and 5.3%(5/94) in TNBC. The prevalence of gBRCA2 mutation was 5.8%(33/570) overall, 6.3%(30/475) in HR+/HER2- BC, 3.2%(3/94) in TNBC. Prevalence in low risk TNBC (>60 years at first BC diagnosis, no known family history of relevant cancer and unilateral breast cancer) was 10.5% (2/19, all 2 patients had gBRCA2 mutation). Prevalence in low risk HR+/HER2- (>40 years at first BC diagnosis, no known family history of relevant cancer and unilateral breast cancer) was 5.9% (18/307, 17 patients had gBRCA2 mutation). The overall prevalence of gBRCA1/2 pathogenic mutation in Korean patients with low risk HER2-negative advanced BC was 6.1%. The result of somatic mutation, treatment patterns and clinical outcome according to gBRCA1/2 mutation will be further analyzed. Conclusions The prevalence of gBRCA mutation among Korean patients with HER2-negative advanced BC classified as low risk (6.1%) in this study supports routine testing of gBRCA mutation in this population. Citation Format: Hee Kyung Ahn, Jee Hung Kim, Mirae Kim, Seri Park, Su-Jin Koh, Joo Hyuk Sohn, Myoung Joo Kang, Kyung Hae Jung, Kyoung Eun Lee, Jieun Lee, Sung Ae Koh, Yee Soo Chae, Jae Ho Byun, In Hae Park, Hee-Jun Kim, Jee Hyun Kim, Han Jo Kim, Joo Young Jung, Jung Lim Lee, Yoon Young Cho, Kyong Hwa Park, Ji-Yeon Kim, Seock-Ah Im, Yeon Hee Park. Prevalence of germline BRCA mutations in unselected Korean patients with HER2-negative breast cancer: A Prospective cohort study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-03-14.