Participant will also be given a study drug diary. Participant should write down each dose of study drug that participant takes, when participant takes it, and if participant misses or vomit any doses. If participant misses or vomits a dose of rigosertib, participant should not make up the dose. Participant should take the next scheduled dose as planned. Every 4 weeks for 12 weeks, then every 8 weeks thereafter, participant should bring any leftover rigosertib capsules and participant's study drug diary with participant to the clinic.