Duration of spleen response. Includes randomized and extension phases for patients randomized to ruxolitinib; crossover patients are not included. Duration of maintenance was estimated only for patients who achieved a ≥35% reduction in spleen volume. The start date was defined as the first spleen volume measurement that was a ≥35% reduction from baseline (minimum of 12 weeks [ie, first on-treatment assessment by magnetic resonance imaging]), and the end date was the first measurement that was no longer a ≥35% reduction and that was a >25% increase above the nadir.