BESREMi FDA Approval: First New ET Drug in Three Decades

The FDA approved PharmaEssentia’s BESREMi (ropeginterferon alfa-2b-njft) for adults with essential thrombocythemia (ET) on August 31, handing the rare blood cancer its first new treatment in nearly three decades. The approval widens BESREMi’s label beyond polycythemia vera (PV), the related myeloproliferative neoplasm (MPN) the drug has treated since its 2021 US approval.

ET makes the bone marrow overproduce platelets, which raises the risk of blood clots, stroke, and heart attack, and patients often need years of ongoing management. BESREMi uses monopegylation to stretch its half-life, so the long-acting interferon can target disease-driving cells in the bone marrow over months rather than the short window of standard interferon.

In the Phase 3 SURPASS-ET trial of 174 patients resistant or intolerant to hydroxyurea, BESREMi produced a durable modified ELN response in 42.9% of patients at months 9 and 12, versus 6.0% for anagrelide (p=.0001), a sevenfold advantage. The interferon also cut thromboembolic and cardiovascular events to 1.1%, against 10% for anagrelide, and shrank the JAK2 V617F allele burden, evidence that it works at the source of the disease instead of just lowering platelet counts. On safety, the tradeoff is interferon’s known flu-like symptoms and fatigue, but tolerability still favored BESREMi: 5.5% of patients discontinued for adverse events versus 18.8% on anagrelide, and treatment-related serious adverse events ran 2.2% versus 10.0%.

The label covers adults regardless of genotype or disease status, including newly diagnosed patients not yet on cytoreductive therapy. A companion single-arm North American study, EXCEED-ET, showed responses across the JAK2, CALR, and MPL driver mutations, supporting the broad label, and BESREMi holds orphan drug designation for both PV and ET. The incumbent anagrelide dates to 1997, and hydroxyurea, the other mainstay, is even older, which is why the first-new-drug-in-decades framing matters. PharmaEssentia is based in Taipei and trades only on the Taiwan exchange (TWSE: 6446), so there is no US ticker to follow; US sales run through its Burlington, Massachusetts subsidiary. Taiwan and Japan cleared BESREMi for ET earlier this year, making the United States the newest major market in the company’s MPN franchise, and PharmaEssentia retains global rights to BESREMi across all indications.

BESREMi’s PV business also got a new competitor this week, when the FDA approved Protagonist’s rusfertide for the sister indication polycythemia vera; in ET, by contrast, BESREMi faces essentially no direct competition. PharmaEssentia announced the approval on August 31, and the drug is expected to be available in the US immediately.

What to watch next: launch execution and whether BESREMi can convert its head-to-head win over anagrelide into real ET market share now that the label is broad enough to cover newly diagnosed patients.