In CCA, various genes have been reported to have frequent methylation, including MLH1, DCLK1, CDO1, ZSCAN18, ZNF331, p14, p16, DAPK, CCND2, CDH13, GRIN2B, RUNX3, TWIST1, EGFR and LKB1 [45]. This evidence concerns the gene CDO1 and cholangiocarcinoma.