Pathogenic variants (PVs) in the BRCA1 and BRCA2 genes are associated with an increased lifetime risk of pancreatic ductal adenocarcinoma (PDAC), and more recently have been associated with increased risk of biliary tract cancers (BTC). This study assessed the prevalence, age and gender distribution of PDAC/BTC cases in families known to carry a BRCA1/2 PV compared to those of the Irish population. A review of all families referred to a national genetics clinic from 09/11/1997 to 01/06/2018 was performed. The BOADICEA algorithm was used to estimate the probability that an untested relative of a known BRCA1/2 PV carrier with PDAC was a carrier. We reviewed 3252 family pedigrees, 1193 contained a proband who underwent testing for BRCA1/2 based on Manchester score ≥ 15. Among 128 BRCA2 PV-positive families, 27 (21%) contained a 1st/2nd/3rd-degree relative with PDAC, while of 116 BRCA1 PV-positive families, 11 (9%) contained a 1st/2nd/3rd-degree relative with PDAC. Within these 38 families, 25 patients with PDAC had ≥ 50% likelihood of being a BRCA1/2 PV carrier. This cohort had a median age at diagnosis of 55 years (range 33-75), with a mean (55 years) lower than 8364 patients with PDAC identified through the National Cancer Registry of Ireland (71 years, p < 0.0001). Six BRCA2 positive (5%) and 2 BRCA1 positive pedigrees (2%) included an individual with BTC; median age at diagnosis was 65 years (range 33-99). PDAC and BTC are prevalent in Irish families harbouring a BRCA2 PV and are associated with early-onset malignancy. This supports current guidelines recommending universal germline testing for PDAC patients.
Keywords: BRCA1; BRCA2; Biliary tract cancer; Genetic testing; Irish population; Pancreatic cancer.