ARID1A and cholangiocarcinoma: Mutations in several epigenetic genes with high frequency have been reported in CCA, including the oncogene IDH1/2 (1%–15%) and the tumor suppressor genes BAP1 (1%–23%), ARID1A (2%–11%), ARID2 (1%–5%), and PBRM1 (1%–23%) (12), as well as general epigenetic dysregulation regardless of the mutation status of these genes, such as widespread DNA hypermethylation (13).