The use of intron-a (rIFN-α) and Pegasys has been extensively studied in patients with PV and reported rates of discontinuation in the first year of therapy range from 14-40%. Objective hematologic responses are seen in approximately 80% of treated patients and achievement in complete phlebotomy free state in 60% of PV patients. Trials of Pegasys in the treatment of PV have further demonstrated major molecular responses of 19% and complete eradication of JAK2V617F in 14-24% of patients. Although hematologic remission can often be achieved within months of starting rIFN-α treatment, molecular responses require longer term administration and are rarely seen before completion of 12 months of therapy. Additionally, sustained molecular remissions have been documented in patients that have discontinued therapy for up to 30 months of follow up. In a retrospective review of 118 MPN patients receiving Pegasys throughout multiple MPN centers included 55 PV patients with an ORR of 87% (54% CR, 33% PR) by ELN criteria [21]. In this review, the most common non-hematologic toxicities were Grade 1-3 fatigue in 24 patients (20%), Grade 1 liver function test (LFT) elevation in 7 (6%), and Grade 1-2 skin/allergic reaction in 6 (5%). Adverse effects leading to discontinuation were primarily non-hematologic, although one patient (<1%) discontinued Pegasys therapy due to Grade 2 anemia.