Clinical Impact of Hypomethylating Agents in the Treatment of Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematologic diseases, mainly affecting the elderly, characterized by unilinear or multilinear peripheral cytopenia, bone marrow ineffective haemopoiesis, and a varying risk of progression to acute myeloid leukemia (AML). On the basis of the prognostic score systems currently used, MDS patients are generally classified as having higher risk (HR) or lower risk (LR) MDS. Two drugs, azacitidine (AZA) and decitabine (DAC), defined, because of their proven mechanism of action, as DNA methyltransferase inhibitors (DNMTIs), or hypomethylating agents (HMAs), have proven effective in improving peripheral cytopenias and quality of life, reducing or eliminating transfusion need, delaying leukemic evolution, and (only for AZA) prolonging overall survival (OS). HMAs are currently the first therapeutic choice for MDS patients who are not candidates for allogeneic hematopoietic stem cell transplantation (allo-HSCT). HMAs have also been used before and after allo-HSCT, but their role in this setting needs to be confirmed by larger studies. Although data from several clinical and biological studies might help to identify patients with a higher probability to respond to HMAs, to date this treatment should not be denied to any HR MDS patient. Several attempts have been made to combine HMAs with other therapeutic agents, and these results await confirmation by further studies.