TET1 and cancer: In agreement with their proposed ‘demethylation’ role, mutations in TET1 and TET2, which are frequent in many cancers, are associated with a hypermethylated promoter phenotype (as seen in acute myeloid leukemia), as are ‘de novo’ mutations in the IDH1/2 genes that result in the production of 2-hydroxyglutarate instead of α-ketoglutarate, a competitive inhibitor of TET enzyme activity [6].