CDKN2A gene functions as an important tumor suppressor in various human malignancies including cholangiocarcinomas, and its activation prevents carcinogenesis via induction of cell growth arrest and senescence. Majority of the CDKN2A mutations span exon 2 and result in loss or decreased binding to CDK4/6 leading to uncontrolled cell growth through inactivation of Rb and p53 pathways. Somatic mutations of CDKN2A are present in various tumor types including cholangiocarcinomas where they appear to be more common in extrahepatic cholangiocarcinomas (up to 15%) than in intrahepatic ones. However, epigenetic silencing of CDKN2A by hypermethylation is more frequent, and the frequency ranges from 17% to 83% in different studies. Of note, inactivation of CDKN2A may portend poor clinical outcome according to some studies. However, correlation with other clinical and lab findings is necessary.