5-Azacytidine or azacitidine (1) and 5-aza-2′-deoxycytidine or decitabine (2) (Figure 2) are indeed the only two DNMT inhibitors (DNMTi) approved by the USA Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of acute myeloid leukemia (AML), chronic myelomonocytic leukemia (CMML) and myelodysplastic syndromes (MDS) [17]. Here, DNMT1 is linked to chronic myelomonocytic leukemia.