FDA Approves Ropeginterferon Alfa-2b in Essential Thrombocythemia

Ropeginterferon alfa-2b-njft (Besremi; PharmaEssentia) has become the first new treatment approved for essential thrombocythemia (ET) in nearly 3 decades, giving patients with this rare blood cancer a genotype-agnostic option after a long stretch of reliance on older cytoreductive therapies.¹ The FDA approval, announced August 31, extends a drug already used in polycythemia vera (PV) into a second myeloproliferative neoplasm (MPN), raising questions for payers and health systems about how a long-acting interferon fits into an ET treatment landscape that has changed little since anagrelide’s 1997 approval.^1,2

Phase 3 SURPASS ET trial (NCT04285086) data comprised the foundation of this approval.^1,2 The open-label, multicenter, randomized study enrolled 174 adults with ET who had an inadequate response to or were intolerant of hydroxyurea. Patients were randomized to ropeginterferon alfa-2b-njft (n = 91) or anagrelide (n = 83), an antineoplastic interferon³ and a phosphodiesterase 3 inhibitor,⁴ respectively. Ropeginterferon alfa-2b-njft was titrated up from 250 mcg to a 500-mcg maintenance dose administered subcutaneously every 2 weeks. Both study arms also received low-dose aspirin per local practice, which was 75 mg/day to 150 mg/day.²

Efficacy was evaluated via durable Modified European Leukemia Net (ELN) response rates at month 9 and month 12, which encompassed blood count remission, stable or improved spleen size, and freedom from bleeding or clotting events.

What Differentiates Ropeginterferon Alfa-2b-njft?

Ropeginterferon alfa-2b-njft produced a response rate that was just over 10 times higher compared with anagrelide at both time points: 37.4% vs 3.6%. The most common adverse events were anemia, fever, bacterial infection, itching, transaminase elevations, and weight loss. There is a boxed warning for serious autoimmune, infectious, ischemic, and neuropsychiatric disorders attached to the interferon treatment.⁵

Unlike hydroxyurea and anagrelide, which primarily manage platelet counts and symptoms, ropeginterferon alfa-2b-njft is designed using monopegylation technology to target disease-driving cells in the bone marrow, an approach described as addressing disease biology rather than symptoms alone.⁶ The expanded indication also covers adults with ET regardless of genotype or disease status, including treatment-naïve patients.¹

“In my experience, patients need treatment options that not only control blood counts but also address the underlying disease,” said 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, in a statement.¹ “The approval of [ropeginterferon alfa-2b-njft] 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.”

The Significance of This Approval

Topline SURPASS ET results presented at the 2025 European Hematology Association Congress showed an even larger treatment effect than the current data: a 42.9% modified ELN response rate for ropeginterferon alfa-2b-njft vs 6.0% for anagrelide, along with a molecular response in nearly one-third of the ropeginterferon arm, prompting investigators to suggest the drug could carry disease-modifying potential.⁷ In addition, data on the calreticulin-mutant ET agent INCA33989 similarly cited SURPASS ET as potentially reshaping the second-line ET landscape.⁸

Pegylated interferons are recommended in the National Comprehensive Cancer Network guidelines across PV, ET, and myelofibrosis, and yet real-world uptake has lagged behind their safety and efficacy data.⁹ For payers and health systems, this approval introduces a second MPN indication for a drug that already carries orphan drug designation.¹

Ropeginterferon alfa-2b-njft is expected to be available immediately, and its regulatory approval follows earlier such approvals in Japan and Taiwan.

References

1. FDA approves PharmaEssentia’s Besremi (ropeginterferon alfa-2b-njft) for adults with essential thrombocythemia, a rare blood cancer. News release. BusinessWire. August 31, 2026. Accessed September 1, 2026. https://www.businesswire.com/news/home/20260831907028/en/FDA-Approves-PharmaEssentias-BESREMi-ropeginterferon-alfa-2b-njft-for-Adults-with-Essential-Thrombocythemia-A-Rare-Blood-Cancer
2. FDA approves treatment for essential thrombocythemia. News release. FDA. August 31, 2026. Accessed September 1, 2026. https://www.fda.gov/drugs/news-events-human-drugs/fda-approves-treatment-essential-thrombocythemia
3. Ropeginterferon alfa-2b-njft (subcutaneous route). Mayo Clinic. Updated August 1, 2026. Accessed September 1, 2026. https://www.mayoclinic.org/drugs-supplements/ropeginterferon-alfa-2b-njft-subcutaneous-route/description/drg-20526931
4. Anagrelide. MedlinePlus. October 15, 2023. Accessed September 1, 2026. https://medlineplus.gov/druginfo/meds/a601020.html
5. Besremi pen. Prescribing information. PharmaEssentia; 2026. Accessed September 1, 2026. https://besremi.com/pv/
6. 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
7. Mattina C. EHA plenary abstracts zoom in from investigational drugs to molecular signatures. AJMC^®. June 14, 2025. Accessed September 1, 2026. https://www.ajmc.com/view/eha-plenary-abstracts-zoom-in-from-investigational-drugs-to-molecular-signatures
8. McCormick B, Mascarenhas J. INCA33989 shows disease-modifying potential with favorable safety in essential thrombocythemia: John Mascarenhas, MD. AJMC. June 26, 2025. Accessed September 1, 2026. https://www.ajmc.com/view/inca33989-shows-disease-modifying-potential-with-favorable-safety-in-essential-thrombocythemia-john-mascarenhas-md
9. Kaltwasser J. Pegylated interferons have promise but also unmet potential in MPNs. AJMC. March 26, 2024. Accessed September 1, 2026. https://www.ajmc.com/view/pegylated-interferons-have-promise-but-also-unmet-potential-in-mpns