Introduction/Background BRCA1/2-germline variant carriers are offered timely risk-reducing salpingo-oophorectomy to prevent high-grade serous carcinoma (HGSC). However, a small percentage of women still develop peritoneal HGSC after RRSO, even when no abnormalities are detected at RRSO. We investigated the incidence and median time to peritoneal HGSC after normal RRSO in asymptomatic BRCA1/2-GPV carriers.

Methodology We included BRCA1/2-GPV carriers from the Hereditary Breast and Ovarian cancer in the Netherlands (HEBON) cohort, who underwent RRSO between 1995 and 2018. Pathology results were retrieved from the Dutch pathology registry (PALGA). Histopathological review was performed to confirm the diagnosis of peritoneal HGSC after RRSO. Women with STIC or HGSC at RRSO were excluded. Follow-up started at date of RRSO and ended at date of diagnosis of peritoneal HGSC, date of death or date of last PALGA search. Incidence and median time to peritoneal HGSC after normal RRSO were calculated.

Results A total of 2519 women were included, of whom 1594 carried a BRCA1-GPV, 922 a BRCA2-GPV and 3 women both a BRCA1- and BRCA2-GPV. Median age at RRSO was 43.2 years (range: 25.3–75.6) for BRCA1-GPV and 47.3 years (range: 25.6–78.3) for BRCA2-GPV. During a median follow-up of 13.5 years, 18 (1.1%) BRCA1-GPV carriers and one (0.1%) BRCA2-GPV carrier developed peritoneal HGSC after normal RRSO. Median age at HGSC diagnosis was 60.1 years (range: 46.5–75.7). Median time from RRSO to peritoneal HGSC diagnosis was 8.2 years (range: 2.2–16.6). Results regarding risk factors and survival will be available by the time of the congress.

Conclusion Incidence of peritoneal HGSC in asymptomatic BRCA1/2-GPV carriers after normal RRSO was low and occurred mostly in BRCA1-GPV carriers. A wide time interval of RRSO to peritoneal HGSC was observed, even up to 16 years after RRSO. Our results provide valuable information for the counselling of BRCA1/2-GPV carriers planning to undergo RRSO.

Disclosures The authors have no conflicts of interest to disclose.