Unexpected finding of a rare pathogenic germline BRCA1 variant in an intrahepatic cholangiocarcinoma using the Oncomine Focus DNA assay: clinical and diagnostic implications

Abstract Background Cholangiocarcinoma (CCA) is a malignant tumor arising from the epithelial cells of the bile ducts and is the second most common liver cancer after hepatocellular carcinoma. Recently, our Institution launched a Comprehensive Genomic Profiling (CGP) program (named FPG500 program), set up to provide a complete molecular characterization through the TruSight Oncology 500 High Throughput (TSO500HT) solution and samples that do not reach pre-set sample quantity and/or quality thresholds required for TSO500HT, are addressed to Oncomine Focus DNA Assay (OFA) and the Archer's FusionPlex Lung Panel (AFL). Methods and results Here we report the case of a patient with iCCA enrolled in the FPG500 program and screened by the orthogonal workflow (OFA/AFL). Although BRCA1 is not among the genes declared in the OFA panel, we unexpectedly detected a pathogenic variant in this gene ( c.5278-2del , rs878853285). Conclusions This case highlights the diagnostic capabilities of CGP, now widely used in both clinical practice and academic setting. The incidental involvement of BRCA1 focuses attention on the role of BRCA genes in biliary tract cancers. Finally, as an orthogonal test confirmed the germline origin of BRCA1 c.5278-2del variant, the germline implications of CGP need to be considered.