Characteristics of breast cancer patients tested for germline BRCA1/2 mutations by next‐generation sequencing in Ramathibodi Hospital, Mahidol University

INTRODUCTION: Germline mutations in BRCA1/2 are the most common cause of hereditary breast and ovarian cancer (HBOC) syndrome. Few studies published during the past decade reported the prevalence of germline BRCA mutations in Asian patients with breast cancer. We aimed to assess the prevalence and characteristics of Thai patients with breast cancer with germline BRCA1/2 mutations. METHODS: We retrospectively reviewed all breast cancer patients who were tested for germline BRCA1/2 mutations during 2014–2018. BRCA mutations were detected using next‐generation sequencing and confirmed using Sanger sequencing. We analyzed the characteristics of patients with or without BRCA mutations. Disease‐free survival (DFS) and the associated factors were determined. RESULTS: Among 67 patients, 12 (18%) were BRCA1/2 carriers (6 each), 4 (6%) harbored variants of uncertain significance, and 51 (76%) were non‐carriers. We discovered two novel BRCA2 frameshift mutations (c.2380delA and c.8855dupT). Mean ages at breast cancer diagnosis of BRCA1, BRCA2, and non‐carriers were 39.8, 46.2, and 42.0 years, respectively. The 12 tumors of BRCA carriers were mainly the luminal‐B subtype. Two of these tumors were HER2‐positive luminal‐B, and the triple‐negative subtype was not detected. After adjusting for stages and luminal subtypes, BRCA carriers experienced worse 3‐year DFS than non‐carriers (81.5% vs. 90.3%, HR 2.04 [0.64–6.49], p = .229). The stage at diagnosis was the sole factor significantly associated with 3‐year DFS (100%, 84.8%, and 72.7%; stages I, II, and III, respectively). CONCLUSION: Thai patients with breast cancer with BRCA1/2 mutations were mainly the luminal‐B subtypes with worse prognosis than those without mutations.