Molecular profile of BRCA-mutated biliary tract cancers

IntroductionPrognosis of biliary tract cancers (BTC) remains dismal and novel treatment strategies are needed to improve survival. BRCA mutations are known to occur in BTC but their frequency and the molecular landscape in which they are observed in distinct sites of BTC remain unknown.Material and methodsTumour samples from 1292 patients with BTC, comprising intrahepatic cholangiocarcinoma (IHC, n=746), extrahepatic cholangiocarcinoma (EHC, n=189) and gallbladder cancer (GBC, n=353), were analysed using next-generation sequencing (NGS). Tumour mutational burden (TMB) was calculated based on somatic non-synonymous missense mutations. Determination of tumour mismatch repair (MMR) or microsatellite instability (MSI) status was done by fragment analysis, immunohistochemistry and the evaluation of known microsatellite loci by NGS. Programmed death ligand 1 expression was analysed using immunohistochemistry.ResultsOverall, BRCA mutations were detected in 3.6% (n=46) of samples (BRCA1: 0.6%, BRCA2: 3%) with no significant difference in frequency observed based on tumour site. In GBC and IHC, BRCA2 mutations (4.0% and 2.7%) were more frequent than BRCA1 (0.3% and 0.4%, p