If participant is found to be eligible to take part in this study, participant will take rigosertib capsules by mouth 2 times each day (1 morning dose, 1 afternoon dose) for 48 weeks. Participant will take participant's morning dose on an empty stomach. Participant's afternoon dose should be taken at about 3:00 pm (±1 hour), at least 2 hours after lunch. Participant should drink at least a ½ gallon of water each day. Rigosertib should be refrigerated.