Safety and Efficacy of Fedratinib in Patients With Primary or Secondary Myelofibrosis

IMPORTANCE Myelofibrosis (MF) is a BCR-ABL-negative myeloproliferative neoplasm characterized by anemia, splenomegaly, debilitating constitutional symptoms, and shortened survival.Fedratinib, a JAK2-selective inhibitor, previously demonstrated clinically beneficial activity in patients with MF in early-phase trials.OBJECTIVE To evaluate the efficacy and safety of fedratinib therapy in patients with primary or secondary (post-polycythemia vera or post-essential thrombocythemia) MF.DESIGN, SETTING, AND PARTICIPANTS Double-blind, randomized, placebo-controlled phase 3 study in 94 sites in 24 countries in which 289 adult patients (Ն18 years of age) with intermediate-2 or high-risk primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF were randomly assigned between December 2011 and September 2012 to once-daily oral fedratinib, at a dose of 400 mg or 500 mg, or placebo, for at least 6 consecutive 4-week cycles. MAIN OUTCOMES AND MEASURESThe primary end point was spleen response (Ն35% reduction in spleen volume from baseline as determined by magnetic resonance imaging or computed tomography) at week 24 and confirmed 4 weeks later.The main secondary end point was symptom response (Ն50% reduction in total symptom score, assessed using the modified Myelofibrosis Symptom Assessment Form). RESULTSThe primary end point was achieved by 35 of 96 (36% [95% CI, 27%-46%]) and 39 of 97 (40% [95% CI, 30%-50%]) patients in the fedratinib 400-mg and 500-mg groups, vs 1 of 96 (1% [95% CI, 0%-3%]) in the placebo group (P < .001).Symptom response rates at week 24 were 33 of 91 (36% [95% CI, 26%-46%]), 31 of 91 (34% [95% CI, 24%-44%]), and 6 of 85 (7% [95% CI, 2%-13%]) in the fedratinib 400-mg, 500-mg, and placebo groups, respectively (P < .001).Common adverse events with fedratinib treatment were anemia, gastrointestinal symptoms, and increased levels of liver transaminases, serum creatinine, and pancreatic enzymes.Encephalopathy was reported in 4 women who received fedratinib 500 mg/d.A diagnosis of Wernicke encephalopathy was supported by magnetic resonance imaging in 3 cases and suspected clinically in 1 case.CONCLUSIONS AND RELEVANCE Fedratinib therapy significantly reduced splenomegaly and symptom burden in patients with MF.These benefits were accompanied by toxic effects in some patients, the most important being encephalopathy of unknown mechanism.Clinical development of fedratinib was subsequently discontinued.