Randomized Study of ON 01910.Na in Refractory Myelodysplastic Syndrome Patients With Excess Blasts

This is a Phase III open-label, randomized, controlled, multicenter study (up to 50 centers). Approximately 270 patients with MDS classified as RAEB-1 and RAEB-2 using the WHO classification and as RAEB-t and chronic myelomonocytic leukemia (CMML) using the FAB classification who failed, became intolerant to, or progressed after treatment with 5-azacitidine or decitabine administered during the past 2 years, will be randomized in a 2:1 ratio into the following 2 treatment regimens: * Best Supportive Care (BSC) + ON 01910.Na 1800 mg/24 hr administered as a 72-hr continuous intravenous (CIV) infusion on Days 1, 2, and 3 of a 2-week cycle (N = approximately 180 patients) * BSC (N = approximately 90 patients). Patients will be stratified at entry by bone marrow (BM) blasts (5% to 19% vs. 20% to 30%). After completing the first eight 2-week cycles (i.e., after 16 weeks of treatment), the frequency of further 72-hr CIV infusions will be decreased to an administration on Days 1, 2, and 3 of a 4-week cycle. Patients will remain treated on study until 2006 International Working Group (IWG) progression criteria are met (i.e., 50% increase of BM blasts or worsening of cytopenias) or until death from any cause, whichever comes first. Patients who progress to Acute Myeloid Leukemia (AML) while on study should be offered either standard treatment for AML or enrollment in an appropriate investigational study if they are eligible. These treatments with their start and end dates should be documented and patient survival time will be documented for all randomized patients. Cross-over of BSC patients to ON 01910.Na after progression will not be allowed. However, patients in the BSC-only group will be allowed, as medically justified, access to low-dose cytarabine 20 mg/m2 subcutaneously (SC) once daily for the first consecutive 14 days of each 28-day cycle, up to 4 cycles, until progression or unacceptable toxicity develops. Low-dose cytarabine will be delayed as needed until recovery of blood counts. All study participants will be allowed, as medically justified, access to RBC and platelet transfusions and to growth factors (erythropoietin, Filgrastim \[G-CSF\]). Hydroxyurea will be allowed to manage blastic crisis with hyperleukocytosis when patients transition to leukemia.