Myelodysplastic/Myeloproliferative Disorder Overlap Syndrome: How Should it be Approached?

The chronic myeloid disorders are typically divided into myelodysplastic syndromes (MDS) and myeloproliferative disorders (MPD). However, there are a group of disorders with overlapping features of MDS and MPD. The World Health Organization has recently reclassified hematologic disorders and included a category of MDS/MPD overlap syndromes, which include chronic myelomonocytic leukemia, atypical chronic myelogenous leukemia, juvenile myelomonocytic leukemia, and MDS/MPD unclassifiable, which includes the provisional entity refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T). These latter 4 disorders remain largely enigmatic in their pathogenesis, have a poor prognosis, and limited therapeutic options. However, the JAK2-V617F mutation has recently been discovered in a large majority of patients with RARS-T and might have future therapeutic implications. The approach to the management of these MDS/MPD overlap syndromes largely relies on extrapolation from the management of other MDS and MPD disorders that are similar to the MDS/MPD overlap syndromes.