It has been reported that reduced 5hmC/TET1 expression is associated with the progression of HCC and that increased 5mC expression positively correlates with HCC invasion and recurrence; this suggests that the DNA methylation/demethylation regulated by the TET family of methylcytosine dioxygenases, may participate in the process of HCC progression [18, 19]. The gene discussed is TET1; the disease is hepatocellular carcinoma.