Low BRCA1 and BRCA2 Germline Mutation Rates in a French-Canadian Population with a Diagnosis of Epithelial Tubo-Ovarian Carcinoma.

OBJECTIVE: Universal genetic testing has become increasingly important in the management of epithelial tubo-ovarian and peritoneal carcinoma. Worldwide, reported incidences of deleterious BRCA mutations vary between 12% and 15%. We sought to evaluate the incidence in our population, given its specific genetic background (French-Canadian ancestry).

METHOD: Mainstream genetic testing was implemented in our service in May 2017 and offered to all patients with epithelial tubo-ovarian or peritoneal carcinomas, except mucinous and borderline tumours. Data were prospectively collected in a database and retrospectively analyzed.

RESULTS: We tested 222 patients in our centre, of whom 183 (82.4%) had high-grade serous carcinoma (HGSC). Overall, 139 patients had no identified mutation (62.6%). Deleterious BRCA1 and BRCA2 mutations were found in 12 patients (5.4%): 6 had BRCA1, and 6 BRCA2 mutations; 11 of these patients had HGSC. Other non-BRCA mutations (ATM, RAD51C, RAD51D, BRIP1, CDH1, MRE11, MSH6, MUTYH, PALB2, and PMS2) were observed in an additional 20 patients (9.0%), of whom 18 had HGSC. A total of 63 different variants of unknown significance (VUS) were found, of which 4 were in the BRCA1 and BRCA2 genes. Deleterious mutations were not identified in clear cell carcinomas, and only 1 was found in low-grade serous carcinoma.

CONCLUSION: In our French-Canadian population, the incidence of deleterious germline BRCA mutations was surprisingly low at 5.4%-less than half that reported in the literature. This may affect patient response to poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi) therapy. Mainstream genetic testing was successfully implemented in our service and facilitated access to genetic testing in our patient population.