TDG and neoplasm: Methylated cytosine residues are demethylated in two sequential steps, involving oxidation of 5-methyl-cytosine (5-mC) to 5-hydroxymethyl-cytosine (5-hmC), catalyzed by the 10–11 translocation (TETs) family of proteins,55, 56, 57 followed by reversion to cytosine through oxidation and base excision repair by thymine DNA glycosylase (TDG).58 TETs are putative tumor suppressors.