The opposing patterns of DNMT3B and MTSS1, the fact that DNMT3B overexpression is associated with poor prognosis, and the demonstration that DNMT3B binds directly to the 5 ́-flanking region of the MTSS1 promoter to downregulate MTSS1 expression [6] implicate MTSS1 as one of the major downstream factors of DNMT3B which may at least in part account for the poor prognosis of DNMT3B-overexpressing AML subsets. This evidence concerns the gene DNMT3B and acute myeloid leukemia.