Azacitidine (Aza) is a cytosine analog and an inhibitor of DNA methyl transferase (DNMT) licensed in Europe as first-line treatment for higher-risk myelodysplastic syndromes, in the US for all types of MDS and frequently used also in other myeloid malignancies, such as acute myeloid [8, 9] Treatment has been confidently associated with prolonged survival in these patient groups [10]. This evidence concerns the gene DNMT1 and myelodysplastic syndrome.