Reductions in JAK2V617F allele burden with ruxolitinib treatment in COMFORT-II, a phase III study comparing the safety and efficacy of ruxolitinib to best available therapy (BAT).

Abstract

6514^ Background: Ruxolitinib is a potent and selective JAK1/2 inhibitor approved for the treatment of myelofibrosis (MF) based on results of the phase 3 COMFORT studies. Ruxolitinib demonstrated rapid and durable reductions in splenomegaly and improved MF-related symptoms and quality of life of patients (pts) with MF. Since one measure of efficacy is molecular response, this analysis correlates changes in mutant allele burden (%V617F) with spleen size reduction in COMFORT-II. Methods: COMFORT-II is a randomized, open-label, phase 3 study comparing ruxolitinib 15 or 20 mg twice daily (BID) with BAT. The primary endpoint was a ≥ 35% reduction in spleen volume from baseline (BL) at week 48. Change in %V617F was measured by allele specific qPCR. Pts were stratified by reduction in %V617F (< 10%, 10-20%, > 20%) and results were correlated with achievement of the primary endpoint. Results: More pts in the ruxolitinib arm had ≥ 10% V617F reductions compared with BAT (41% vs 5%; P = .01; Table). The majority of reductions > 20% were gradual and progressive over the course of the study; 2 pts had rapid reductions from 48% to 1% and 45% to 9% over 48 weeks. In the ruxolitinib arm, significantly more pts with a > 20% V617F reduction achieved the primary endpoint compared with pts with a < 10% reduction (79% vs 30%; P = .004); in each group, gender did not affect spleen response. For pts with < 10% reductions (15 mg BID, n = 16; 20 mg BID, n = 24), the average total daily dose (TDD) was ruxolitinib 29.6 mg; pts with > 20% reductions (15 mg BID, n = 3; 20 mg BID, n = 11) had a TDD of 35.3 mg. Conclusions: Pts who received ruxolitinib had larger reductions in JAK2V617F allele burden compared with BAT. %V617F reductions were gradual over the course of the 48-week study; longer follow-up is needed to determine the extent of allele burden reduction. [Table: see text]