Considering (1) that 5mC and 5hmC have different biological roles, (2) that the activities of the dioxygenase TET enzymes are sensitive to numerous metabolic factors (Vit-C, pH, intermediate metabolites) possibly modified by chemical exposures, (3) that TET1 and TET2 are downregulated in many cancers, and (4) that there is generally a global loss of 5hmC in cancers [94], perhaps adequate measurements of both 5mC and 5hmC could generate early markers of chemically induced carcinogenesis. This evidence concerns the gene TET1 and cancer.