The US FDA has approved Besremi (ropeginterferon alfa-2b-njft) for the treatment of adults with essential thrombocythemia (ET), marking the first new approval in this indication in nearly three decades. PharmaEssentia USA Corporation, a Burlington, Massachusetts-based subsidiary of Taiwan-headquartered PharmaEssentia Corporation (TWSE: 6446), received the decision, which expands Besremi's existing label — the drug has been commercially available for polycythemia vera (PV) since 2021. The label does not specify genotype or prior-treatment requirements, allowing use in cytoreductive therapy-naive adults despite the pivotal SURPASS-ET trial having enrolled patients with inadequate response or intolerance to hydroxyurea.
Besremi is a mono-pegylated, long-acting recombinant interferon alfa-2b administered subcutaneously. Its novel monopegylation technology extends half-life, enabling less frequent dosing. Unlike cytoreductive agents such as hydroxyurea or anagrelide — which primarily reduce platelet counts — ropeginterferon alfa-2b targets disease-driving clonal progenitor cells in the bone marrow via the JAK-STAT signaling pathway, with the potential to reduce JAK2 V617F mutant allele burden over time, the company said.
The approval was based on the global Phase III SURPASS-ET trial (NCT04285086), a multicenter, open-label, randomized, active-controlled study. Published in Lancet Haematology in November 2025, the trial demonstrated superior durable response rates for Besremi versus anagrelide, with reduced thromboembolic events over 12 months of treatment in adults with ET. In the FDA efficacy analysis, 37.4% of Besremi-treated patients achieved a durable modified European LeukemiaNet response at both Months 9 and 12 versus 3.6% with anagrelide. The response definition incorporated blood-count remission, improvement or non-progression of splenomegaly, and absence of bleeding or thrombotic events