On August 31, 2026, the U.S. Food and Drug Administration (FDA) approved ropeginterferon alfa-2b-njft (Besremi, PharmaEssentia) for the treatment of adult patients with essential thrombocythemia (ET).
This is the first new agent approved in the United States for the management of ET since anagrelide (Agrylin) in 1997. It expands on Besremi’s initial November 2021 approval for adult patients with polycythemia vera (PV).
“For nearly 30 years, people living with ET and the physicians treating them had limited treatment innovation. 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,” said Dr. Ruben Mesa, quoted in a PharmaEssentia Press release. Dr. Mesa is the principal investigator of the SURPASS-ET clinical trial and President of the Advocate Health Cancer National Service Line.
Understanding the needs for a new treatment specifically made for essential thrombocythemia
Essential thrombocythemia (ET) is a rare myeloproliferative neoplasm (MPN). It is a type of chronic blood cancer that causes the bone marrow to make too many platelets. ET is frequently linked to genetic mutations in genes such as JAK2, CALR, or MPL.
Too many platelets raise your risk for serious complications, including:
Dangerous blood clots (thrombosis) leading to strokes or heart attacks
Severe bleeding (hemorrhage)
Spleen enlargement (splenomegaly)
Progression into myelofibrosis or secondary acute myeloid leukemia (AML)
Before Besremi, other treatment options for people whose disease resisted initial therapies like hydroxyurea were limited to non-specific agents such as anagrelide.
How Besremi works to treat essential thrombocythemia
Besremi is a new, long-acting monopegylated interferon therapy. It is given as a subcutaneous injection every two weeks.
Unlike older therapies that mainly focus on symptom management and lowering blood counts, Besremi works directly at the root of the disease. It helps lower abnormal cell counts while preventing the formation of more of these abnormal cells, directly reducing the mutant cell burden (such as JAK2 and CALR genetic mutations).
The trial that led to the approval: the SURPASS-ET trial
The FDA approval was primarily supported by findings from the randomized Phase 3 SURPASS-ET trial (NCT04285086), along with data from the Phase 2b EXCEED-ET trial (NCT05482971).
The SURPASS-ET study evaluated 174 adult patients with high-risk ET. The participants were resistant or intolerant to hydroxyurea. Patients were randomized to receive either subcutaneous Besremi or oral anagrelide. Anagrelide is a medication designed to reduce platelet counts and lower the risk of blood clot formation that can risk serious complications like stroke or deep vein thrombosis.
Outcome | Besremi (n = 91) | Anagrelide (n = 83) |
Response Rate (Months 9 & 12) | 37.4% | 3.6% |
Platelet count improvement | 56.0% | 21.7% |
White blood cell count improvement | 73.6% | 13.3% |
Symptom improvement | 71.4% | 33.7% |
Absence of blood clots or bleeding | 84.6% | 51.8% |
Besremi led to less treatment interruptions due to side effects
Compared to anagrelide, Besremi showed a favorable safety profile. During the clinical trials, only 5.5% of people treated with Besremi stopped due to side effects. In comparison, 20% of people treated with anagrelide stopped treatment. Overall, people treated with Besremi hadfewer severe side effects (23.1% vs. 33.8%).
Besremi may lower genetic risk factors
After one year of treatment, Besremi also reduced the genetic abnormalities that led to ET.
JAK2 V617F allele burden: Decreased by an average of 8.06% in the Besremi group, compared to an increase of 3.21% in the anagrelide arm.
CALR allele burden: Decreased by 5.32% with Besremi versus 1.45% with anagrelide.
Blood clot risk: After 12 months, major ET-related thrombotic events (blood clots) occurred in only 1.1% of Besremi-treated patients, compared to 10.0% of anagrelide-treated patients.
Most common side effects of Besremi
The most common side effects of Besremi were:
Elevated liver enzymes
Anemia
Fever
Elevated beta-2 microglobulin in urine
Itching
Weight loss
No fatal adverse events occurred in the Besremi arm of the study.
How is Besremi given?
Besremi is administered subcutaneously once every two weeks. Treatment usually starts at a dosage of 250 mcg at weeks 0 to 2 and increases to 350 mcg at weeks 2 to 4. The targeted maintenance dose is 500 mcg every two weeks. This is adjusted based on patient tolerance and blood counts.
If you have been diagnosed with essential thrombocythemia, talk to your care team to determine if Besremi is an appropriate addition to your treatment plan.
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