Despite there is a slight decrease of TET1 and TET3 in HCC, 5-hmC levels are significantly reduced in HCC tumors than in adjacent normal tissue; further investigations revealed that the reduction of 5-hmC level in HCC is associated with hepatitis B virus (HBV) infection and TET2 deficiency [14, 15]. This evidence concerns the gene TET1 and hepatocellular carcinoma.