The primary objective of this study is to compare overall survival (OS) in patients receiving ON 01910.Na + best supportive care (BSC) to OS of patients receiving BSC in a population of patients with myelodysplastic syndrome (MDS) with excess blasts (5% to 30% bone marrow blasts) who have failed azacitidine or decitabine treatment. This patient population has no available therapy and a short life expectancy (approximately 4 months). The high level of bone marrow activity of ON 01910.Na documented in Phase 1 and 2 studies has the potential to delay substantially the transition of MDS to Acute Myeloid Leukemia(AML), a very significant and severe complication, which shortens survival of these MDS patients.