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Purpose We conducted a phase II study of pegylated interferon alfa-2a (PEG-IFN-α-2a) in patients with essential thrombocythemia (ET) and polycythemia vera (PV). Patients and Methods Seventy-nine patients (40 with PV and 39 with ET) have been treated. Median time from diagnosis to PEG-IFN-α-2a was 54 months in patients with PV and 33 months in patients with ET. Eighty-one percent of patients had received prior therapy. The first three patients received PEG-IFN-α-2a at 450 μg weekly. As a result of poor tolerance, this dose was decreased in a stepwise manner to a current starting dose of 90 μg weekly. Seventy-seven patients are evaluable and have been observed for a median of 21 months. Results The overall hematologic response rate was 80% in PV and 81% in ET (complete in 70% and 76% of patients, respectively). The JAK2V617F mutation was detected in 18 patients with ET and 38 patients with PV; sequential measurements by a pyrosequencing assay were available in 16 patients with ET and 35 patients with PV. The molecular response rate was 38% in ET and 54% in PV, being complete (undetectable JAK2V617F) in 6% and 14%, respectively. The JAK2V617F mutant allele burden continued to decrease with no clear evidence for a plateau. The tolerability of PEG-IFN-α-2a at 90 μg weekly was excellent. Conclusion PEG-IFN-α-2a resulted in remarkable clinical activity, high rates of molecular response, and acceptable toxicity in patients with advanced ET or PV. The ability of PEG-IFN-α-2a to induce complete molecular responses suggests selective targeting of the malignant clone.

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 × 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 JAK2V617F–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.