When half of the patients remaining in the study completed the Week 36 visit and all patients enrolled completed Week 24 or discontinued, the database was frozen and the primary analysis was conducted. Once this was complete, all patients were unblinded and patients who had been randomized to placebo were given the opportunity to cross over to ruxolitinib treatment, provided hematology laboratory parameters were adequate; Patients receiving benefit could continue treatment until the later of marketing approval or when the last randomized patient remaining in the study had completed Week 144 (36 months).