Mutations occurring in TET2 are present in about 30% of aCML cases (14, 104–106); therefore, they are among the most frequent mutations occurring in this disorder, together with SETBP1 and ASXL1. TET2 mutations are invariably linked to a global decrease in the 5hmC mark, which suggests that they represent loss-of-function events. This evidence concerns the gene TET2 and atypical chronic myeloid leukemia, BCR-ABL1 negative.