Biliary tract cancers: Epidemiology, molecular pathogenesis and genetic risk associations

Biliary tract cancers (BTC) are malignancies that arise from the epithelium of the biliary system and comprise the second most common type of hepatobiliary cancer worldwide. BTC are sub-classified as intrahepatic cholangiocarcinoma (iCCA), perhilar/hilar cholangiocarcinoma (pCCA), distal cholangiocarcinoma (dCCA), and gallbladder carcinoma. Due to the differences in their etiologic risk factors, pathogenesis, and molecular and genetic characteristics, each of these subtypes is considered a separate biological entity. The geographic diversity of risk factors for the subtypes of biliary cancers results in profound differences in the worldwide incidence of each. In this article we provide a review of the current epidemiology of BTC and their associated risk factors. Further, we discuss the available evidence for genetic predisposition to BTC and anticipate the results of planned large-scale, genome-wide association studies (GWAS) exploring the inherited sequence variants conferring risk of BTC. These studies may also potentially of reveal important pathogenic mechanisms of the biliary tract cancer subtypes.