This was an open-label, single-center, dose-escalating Phase I study to determine the Dose-Limiting Toxicities (DLTs) and Recommended Phase 2 Dose (RPTD) of ON 01910.Na (rigosertib sodium) administered as a 3 day continuous intravenous (CIV) infusion every 2 weeks (2-week cycles) to up to 28 patients with advanced cancer (12 to 16 in the dose escalation phase and up to 12 additional patients in the dose confirmation phase). The dosing of rigosertib was based on body surface area (BSA), with a starting dose of 50 mg/m2/24 hour for 3 consecutive days.