In the absence of toxicity after at least a 3-week observation period, rigosertib doses were escalated following a Fibonacci scheme with an initial accelerated dose-escalation phase in which 1-patient cohorts received rigosertib for 3 weeks until drug-related Grade 2 toxicity (according to Common Toxicity Criteria for Adverse Events [CTCAE] v.3), excluding alopecia, occurred, at which time 2 additional patients were added to subsequent cohorts. If none of the 3 patients in the cohort experienced DLTs, the dose was escalated by a half-Fibonacci step. If a DLT was seen in the first patient of a cohort, dosing went back a half-step. The next dose level occurred if no DLT was reported in the 3 patients or if no more than 1 DLT occurred in an expanded cohort of 6 patients. If a DLT was seen in 1 of the 3 patients, 3 additional patients were enrolled in the cohort. If DLTs were seen in 2 of 6 patients in a cohort, dose escalation was stopped.