Ropeginterferon alfa-2b for prefibrotic myelofibrosis and lower-risk myelofibrosis requiring cytoreduction.

There is currently no consensus on the optimal treatment of early myelofibrosis (MF). Ropeginterferon alfa-2b (ropeg) is a next-generation monopegylated interferon alfa-2b developed specifically to treat myeloproliferative neoplasms. We conducted a phase 2 study in patients with prefibrotic primary MF (pre-PMF) and Dynamic International Prognostic Scoring System low-/intermediate-1-risk fibrotic PMF or secondary MF (SMF) who required cytoreduction. Ongoing treatment with hydroxyurea was substituted with ropeg (week 0, 250 μg; week 2, 350 μg; week 4 onward, 500 μg every 2 weeks). The primary end points were safety and clinicohematologic complete response (CHCR). Seventy-one patients (40 men and 31 women) with a median age of 60 years (range, 31-86) were enrolled and followed up for a median of 119 weeks (range, 10-131). At weeks 24, 48, and 104, CHCR was achieved in 63.8% (pre-PMF, 74%; fibrotic PMF, 20%; fibrotic SMF, 42.9%), 63.5% (pre-PMF, 69.6%; fibrotic PMF, 25%; SMF, 53.9%), and 70% of patients (pre-PMF, 78.4%; fibrotic PMF, 33.3%; SMF, 50%), respectively. Thrombo-hemorrhagic events were not observed after stopping hydroxyurea. At weeks 24, 48, and 104, reduction in JAK2V617F variant allele frequency (VAF) was observed in 53.1%, 70%, and 67.6% of patients, and reduction in CALR mutant VAF was observed in 52.6%, 42.9%, and 40% of patients, respectively. In 50 evaluable cases at week 104, 13 patients (26%) had reduced bone marrow reticulin fibrosis. There were 3 treatment discontinuations (4.2%) due to adverse events. In conclusion, ropeg was safe and induced CHCR associated with significant molecular responses in patients with early MF. This trial was registered at www.clinicaltrials.gov as NCT04988815.