FDA Approves Ropeginterferon Alfa-2b for Essential Thrombocythemia

The FDA has approved ropeginterferon alfa-2b-njft (Besremi) for adults with essential thrombocythemia (ET), marking the first time an agent has been specifically authorized for ET in the United States in nearly 30 years.¹

The approval is based on the global phase 3 SURPASS-ET trial (NCT04285086), which compared ropeginterferon alfa-2b against anagrelide in adults with high-risk ET who were intolerant of or resistant to hydroxyurea (HU). At the trial's dual assessment points of months 9 and 12, 43% of patients randomized to ropeginterferon achieved a durable modified European LeukemiaNet (ELN) response, a composite requiring simultaneous normalization of blood counts, stable or improved spleen size, symptom improvement, and freedom from bleeding or clotting events, compared with 6% of patients on anagrelide, a difference of 36.5 percentage points (95% CI, 25.4-47.7; P = .0001).²

Secondary results favored ropeginterferon across every domain measured. Peripheral blood count remission was reached by 56% of ropeginterferon-treated patients versus 6% on anagrelide, white blood cell (WBC) count control was achieved by 74% versus 13%, and platelet control was reached by 56% versus 22%. Spleen size stabilized or improved in 88% of the ropeginterferon group compared with 54% on anagrelide, and total symptom burden improved in 71% versus 34%.

Patients on ropeginterferon were also considerably more likely to remain free of hemorrhagic or thrombotic complications during the study, at 85% versus 52% for those on anagrelide. On the molecular side, mean JAK2 V617F allele burden fell by 21.3% among ropeginterferon-treated patients while rising by 12.3% in the anagrelide arm, and nearly a third of evaluable ropeginterferon patients reached a partial molecular response, an outcome no anagrelide-treated patient achieved.²

"For nearly 30 years, people living with ET and the physicians treating them have had limited treatment innovation," Ruben Mesa, MD, principal investigator of the SURPASS-ET trial and president of Advocate Health's Cancer National Service Line, which includes Atrium Health Levine Cancer Institute and the Comprehensive Cancer Center at Atrium Health Wake Forest Baptist, stated in a news release.² "In my experience, patients need treatment options that not only control blood counts but also address the underlying disease. The approval of Besremi provides an important new treatment option that is supported by strong clinical evidence and that also works at the source of the disease rather than solely managing symptoms."

Ropeginterferon alfa-2b-njft is a long-acting, monopegylated interferon alfa therapy built to have an extended half-life so it can be dosed every two weeks. Rather than only lowering platelet counts, the drug is designed to act on the malignant clone in the bone marrow.¹

Safety of Ropeginterferon Alfa-2b in Essential Thrombocythemia

Because ropeginterferon alfa-2b belongs to the interferon alfa class, its label carries a boxed warning that these products may cause or worsen fatal or life-threatening neuropsychiatric, autoimmune, ischemic, and infectious disorders. The prescribing information calls for close clinical and laboratory monitoring and directs clinicians to withdraw therapy if symptoms of these conditions persist or worsen, noting that in most, though not all, cases the disorders resolve once treatment stops.^1,3

In the SURPASS-ET trial, ropeginterferon was better tolerated than anagrelide across most safety measures: grade 3 or higher adverse events occurred in 23% of patients on ropeginterferon versus 34% on anagrelide, serious adverse events occurred in 14% versus 30%, and treatment discontinuations occurred in 5% versus 20%. No deaths occurred among patients treated with ropeginterferon, while three patients died on anagrelide, from acute myocardial infarction, pneumonia, and COVID-19-related pneumonia, respectively. Cerebral infarction occurred in four patients on anagrelide and none on ropeginterferon.³

Design of the Pivotal SURPASS-ET Trial

SURPASS-ET is an open-label, randomized, active-controlled phase 3 study that enrolled 174 adults with high-risk ET, HU intolerance or resistance, and a WBC count above 10 × 10⁹ cells/L. Patients were randomized 1:1, stratified by baseline platelet count, symptom score, and country, to subcutaneous ropeginterferon alfa-2b, initiated at 250 μg and titrated toward a target of 500 μg every two weeks, or to oral anagrelide, dosed and titrated as tolerated. Median follow-up was 12.5 months. Most enrollees were Asian (96%), the median age was in the early sixties, and roughly a third of patients in each arm had a prior history of thrombosis.²

Supporting evidence for extending the approval to patients regardless of genotype or treatment history comes from EXCEED-ET, a single-arm, multicenter phase 2b study conducted in North America in 91 adults with ET, including 67 who were treatment-naive and 24 with prior HU exposure. Across the study population, 60.2% of patients achieved a modified ELN response between months 10 and 12, including 68.0% of treatment-naive patients and 33.4% of those with prior HU exposure, and no patient experienced a bleeding or thrombotic event during that assessment window.⁴

"Today's FDA approval of Besremi for ET is a significant advancement for patients and reflects PharmaEssentia's longstanding commitment to advancing innovative therapies for people living with myeloproliferative neoplasms," Ko-Chung Lin, PhD, founder and chief executive officer of PharmaEssentia, the developer of ropeginterferon alfa-2b, stated in a news release. "We have been working closely with the FDA, healthcare providers, advocacy organizations and payers to bring this important treatment option to the ET community."¹

References

1. PharmaEssentia USA Corporation. FDA approves PharmaEssentia's BESREMi (ropeginterferon alfa-2b-njft) for adults with essential thrombocythemia, a rare blood cancer. Business Wire. Published August 31, 2026. Accessed August 31, 2026. https://tinyurl.com/394nvmun

2. Mesa R, Gill H, Zhang L, et al; SURPASS-ET Study Group. Ropeginterferon alfa-2b in hydroxyurea-intolerant or hydroxyurea-refractory essential thrombocythaemia (SURPASS ET): a multicentre, open-label, randomised, active-controlled, phase 3 study. Lancet Haematol. 2025;12(11):e862-e875. doi:10.1016/S2352-3026(25)00264-9

3. BESREMi (ropeginterferon alfa-2b-njft) [prescribing information]. Burlington, MA: PharmaEssentia USA Corporation; 2026.

4. Reeves BN, El Chaer F, Foltz L, et al. Ropeginterferon alfa-2b-njft treatment in essential thrombocythemia across different driver mutations: results from a North American, single-arm, multicentre study (EXCEED-ET). Lancet Reg Health Am. 2026;61:101529. doi:10.1016/j.lana.2026.101529