Pegylated interferon alfa-2a for polycythemia vera or essential thrombocythemia resistant or intolerant to hydroxyurea

Prior studies have reported high response rates with recombinant interferon-α (rIFN-α) therapy in patients with essential thrombocythemia (ET) and polycythemia vera (PV). To further define the role of rIFN-α, we investigated the outcomes of pegylated-rIFN-α2a (PEG) therapy in patients with ET/PV previously treated with hydroxyurea (HU). The Myeloproliferative Disorders Research Consortium (MPD-RC) 111 study was an investigator-initiated, international, multicenter, phase 2 trial evaluating the ability of PEG therapy to induce complete (CR) and partial (PR) hematologic responses in patients with high-risk ET/PV who were either refractory or intolerant to HU. The study included 65 patients with ET and 50 patients with PV. The overall response rate ORR (CR / PR) at 12 months was 69.2% (43.1% / 26.2%) in ET, and 60% (22%/38%) in PV patients. CR rates were higher in CALR mutated ET patients (56.5% vs. 28.0%, p= 0.01) as compared to subjects lacking a CALR mutation. The median absolute reduction in JAK2V617F variant allele fraction (VAF) was -6% (range -84%-47%) in patients achieving a CR versus +4% (range -18%-56%) in patients with PR/non-response (NR). Therapy was associated with a significant rate of adverse events (AE), most were manageable, and PEG discontinuation due to AEs occurred only in 13.9% of subjects. We conclude that PEG is an effective therapy for patients with ET/PV who were previously refractory and/or intolerant to HU