Lenalidomide plus prednisone results in durable clinical, histopathologic, and molecular responses in patients with myelofibrosis

Purpose: To investigate the safety and efficacy of the combination of lenalidomide and prednisone in patients with myelofibrosis (MF). Patients and Methods: Forty patients with MF were treated. Therapy consisted of lenalidomide 10 mg/d (5 mg/d if baseline platelet count < 100 x 10⁹/L) on days 1 through 21 of a 28-day cycle for six cycles, in combination with prednisone 30 mg/d orally during cycle 1, 15 mg/d during cycle 2, and 15 mg/d every other day during cycle 3. Lenalidomide therapy was continued indefinitely in patients exhibiting clinical benefit. Results: The median follow-up was 22 months (range, 6 to 27). Responses were recorded in 12 patients (30%) and are ongoing in 10 (25%). The median time to response was 12 weeks (range, 2 to 32). According to the International Working Group for Myelofibrosis Research and Treatment consensus criteria, three patients (7.5%) had partial response and nine patients (22.5%) had clinical improvement durable for a median of 18 months (range, 3.5 to 24+). Overall response rates were 30% for anemia and 42% for splenomegaly. Moreover, 10 of 11 assessable responders who started therapy with reticulin fibrosis grade 4 experienced reductions to at least a score of 2. All eight JAK2^V617F-positive responders experienced a reduction of the baseline mutant allele burden, which was greater than 50% in four, including one of whom the mutation became undetectable. Grade 3 to 4 hematologic adverse events included neutropenia (58%), anemia (42%), and thrombocytopenia (13%). Conclusion: The combination of lenalidomide and prednisone induces durable clinical, molecular, and pathologic responses in MF.