CDO1 and cholangiocarcinoma: Methylation of the CDO1 promoter region has been found in esophageal cancer [8, 10], gastric cancer [8], colorectal cancer [8], cholangiocarcinoma [11], lung cancer [8, 12], breast cancer [8], bladder cancer [8], prostate cancer [13], endometrial cancer [14], and hepatitis B virus-related hepatocellular carcinoma (HBV-related HCC) [15].