This study is under Molecular and Cellular Characterization of Myelodysplastic Syndromes (MDS) (eProtocol 15369). The purpose of this proposed study is to analyze existing samples taken from participants participating in a clinical trial evaluating the efficacy and safety of investigational agent ON 01910.Na (eProtocol 16214). This study will use existing blood and marrow samples to determine the rate and duration of objective hematologic and marrow responses, and duration of progression-free survival in ON01910.Na-treated MDS patients.