While responses to hypomethylating agents (HMAs) in IDH and TET2 mutated myeloid neoplasms did not result in much better responses than in unselected MDS/AML patients, the development of selective inhibitors of mutated IDH1 and IDH2 is a success story of targeted therapy in these MDS/AML genotypes. This evidence concerns the gene TET2 and myelodysplastic syndrome.