FDA Approves BESREMi for Essential Thrombocythemia (ET)

By David Wallace | September 13, 2026

The FDA approved BESREMi for essential thrombocythemia on August 31, 2026, giving adults with ET their first new FDA-approved treatment in nearly 30 years. BESREMi (ropeginterferon alfa-2b-njft) is a long-acting interferon given by injection every two weeks.

If hydroxyurea is not controlling your disease or its side effects are becoming difficult, BESREMi offers another option to discuss with your hematologist. Approval alone does not mean you need to switch from a treatment that is working.

Recent September updates add longer follow-up and physician perspectives to the original approval results. They also sharpen a question patients increasingly ask: can treatment reduce the abnormal cells driving ET, as well as improve blood counts?

BESREMi for essential thrombocythemia: approval at a glance

Question	Answer
What was approved?	BESREMi, the brand name for ropeginterferon alfa-2b-njft
When?	August 31, 2026
Who is it approved for?	Adults with essential thrombocythemia
What kind of medicine is it?	A long-acting interferon
How is it taken?	An injection under the skin every two weeks
What was the main study?	SURPASS-ET, involving 174 adults
What was the main result?	37.4% met the combined response goal with BESREMi, compared with 3.6% with anagrelide
What should patients keep in mind?	Treatment requires monitoring and carries a boxed warning for potentially serious side effects

The response goal included blood counts, spleen findings and freedom from clotting or bleeding events at both months 9 and 12. More on what that means below.

Why this matters for people living with ET

ET is a chronic blood cancer within the family of myeloproliferative neoplasms, or MPNs. The bone marrow makes too many platelets. Treatment decisions take into account the risk of blood clots and bleeding, symptoms and other health concerns, rather than relying on the platelet number alone. Our ET overview explains the basics.

For years, patients have discussed options such as hydroxyurea, anagrelide and interferon with their physicians. Interferon has been used for ET before this approval. What changes now is that BESREMi has an FDA-approved use specifically for adults with ET.

Dr Ruben Mesa on what comes next

In a September 7 CancerNetwork interview, Ruben Mesa, MD, FACP, the principal SURPASS-ET investigator, emphasized both blood-count control and the treatment’s effect on the disease-driving clone, the population of abnormal cells descended from a mutated stem cell.

“We hope this will lead to longer and better outcomes for these patients.”

His wording matters. The molecular findings are promising, but whether they translate into longer survival or less progression still needs to be established. In a September 11 Blood Cancers Today interview, Mesa also discussed future studies of earlier treatment and combinations with mutation-targeted medicines. These remain research directions, not established combination regimens for routine ET care.

My perspective as an MPN patient advocate

Living with PV since 2009 has taught me to ask what a treatment will change in daily life. Better counts matter. So do fatigue, side effects and cost. I want ET patients to understand what BESREMi may offer and what questions still need answers.

How BESREMi works and what molecular remission means

BESREMi belongs to the interferon treatment family. It affects cell signaling and can lower elevated blood counts. Researchers also measure its effect on mutations associated with ET, including JAK2, CALR and MPL.

These terms describe different results:

• Blood-count response: platelets and other blood counts reach the study’s specified targets.
• Molecular response: the measured mutation burden falls enough to meet a defined research threshold. Variant allele frequency, or VAF, is the proportion of tested copies of a gene carrying the mutation. It is not a direct percentage of all cancer cells in the body.
• Complete molecular remission: the tracked mutation is no longer detectable by the test used. The result depends on that test’s sensitivity and does not prove that every abnormal cell has disappeared.

A partial molecular response is not complete molecular remission. Neither automatically establishes a cure or means treatment can stop. For ET, the remaining question is how reliably these molecular changes predict fewer complications, less progression to myelofibrosis or leukemia, and longer survival.

What did the SURPASS-ET trial find?

SURPASS-ET compared BESREMi with anagrelide in 174 adults with high-risk ET. Participants had already tried hydroxyurea and either could not tolerate it or had an inadequate response. They also had elevated white blood cell counts when entering the study.

The main question was whether patients could meet a combined treatment goal at both nine and twelve months. Researchers call this a durable modified European LeukemiaNet (ELN) response. It required:

• Platelets and white blood cells within the study’s target ranges.
• Improvement or no worsening of an enlarged spleen.
• No clotting or bleeding events during the assessment period.

In the FDA’s analysis, 37.4% of patients taking BESREMi met this goal, compared with 3.6% taking anagrelide.

Think of that as about 37 out of 100 versus about 4 out of 100 meeting every part of a demanding goal. It does not mean that everyone outside that group received no benefit. A patient might improve in one area without meeting the full definition.

You may also see figures of about 43% versus 6% in the published trial. Those come from a different analysis of the same study. The FDA analysis treated early withdrawals and use of prohibited medicines as nonresponses. We use the approval figures here so readers have one consistent comparison.

What about preventing blood clots?

The study observed fewer clotting events with BESREMi, an encouraging finding. However, the results do not establish a long-term reduction in strokes, heart attacks or death. They are not a reason to stop prescribed aspirin or other clot-prevention treatment without talking with your clinician.

Do these results apply to someone newly diagnosed?

The approval covers adults with ET without requiring previous hydroxyurea treatment or a particular mutation. The strongest randomized evidence, however, came from patients who had already tried hydroxyurea. Most SURPASS-ET participants were Asian. Those details matter when applying the results to other patients.

A separate North American study, EXCEED-ET, included 91 adults, both previously untreated patients and people who had received hydroxyurea. Its durable combined response rate was 60.2%, assessed at months 10 and 13. Everyone received BESREMi, so it cannot establish superiority over another medicine for newly diagnosed patients. Its response percentage should not be compared directly with SURPASS-ET.

At month 13, molecular responses were reported in 7 of 20 evaluable patients with JAK2 mutations, 4 of 25 with CALR and 2 of 8 with MPL. These small subgroups support further study across mutation types; they do not provide a dependable prediction of an individual patient’s response. The figures describe molecular responses, not rates of complete molecular remission.

EXCEED-ET was published online June 10, 2026, in the September journal collection. It is useful supporting research, but it is not a study first released after the August approval.

The two-year SURPASS-ET follow-up also helps explain why researchers are studying how responses develop over time.

What the September 2026 updates add

Blood count control through two years

PharmaEssentia’s September 9 SOHO meeting announcement reported that patients continuing BESREMi in the SURPASS-ET extension maintained blood-count control through two years, with further reductions in JAK2 mutation burden. Patients who switched from anagrelide after the first year also showed improved counts and lower JAK2 burden. Some two-year findings had already been presented at EHA in June.

These observations help address durability. Because patients could switch treatments and the extension followed selected continuing participants, it does not retain the original randomized comparison unchanged.

Experience in community oncology practices

The same announcement described a retrospective review of 55 US patients with ET. BESREMi was usually started after an earlier treatment, although first-line use was also observed. Blood counts and response measures showed favorable trends.

This small, nonrandomized study adds information about everyday practice. It cannot prove superiority over another therapy. These SOHO findings are conference-level evidence summarized by the manufacturer; longer-term analyses remain ongoing.

How is BESREMi given for ET?

BESREMi is injected under the skin. The recommended ET starting schedule is:

Timing	Recommended dose
First injection	250 micrograms (mcg)
Two weeks later	350 mcg
At week four	500 mcg
Ongoing treatment	500 mcg every two weeks, unless changed for safety or tolerability

Your hematologist may lower or pause a dose if side effects develop. Injection training is part of getting started. BESREMi is supplied in a prefilled syringe and a prefilled pen.

The ET and PV schedules differ. The every-four-week option you may have heard about applies to the PV instructions. The approved ET schedule remains every two weeks unless a change is needed for safety or tolerability. Ask your team to explain your own plan, and do not adjust the dose yourself.

BESREMi side effects and monitoring

Side effects deserve an honest conversation before treatment. Common problems reported in the ET study included increased liver enzymes, anemia, fever, bacterial infections, itching and weight loss. Some changes show up in laboratory tests before you notice symptoms.

BESREMi carries a boxed warning, the FDA’s most prominent prescription-drug warning. Interferon can cause or worsen serious, sometimes life-threatening problems involving mental health, autoimmune disease, reduced blood supply to tissues and infections.

Before prescribing, your team should review your health history, medicines, mood and pregnancy plans. The medicine must not be used in certain people, including those with a history of severe psychiatric illness, certain serious autoimmune conditions, moderate or severe liver impairment, an allergy to its ingredients, or transplant recipients taking immunosuppressants. The full prescribing information and Medication Guide explain the restrictions and risks.

Ask for a written monitoring plan. Blood counts are checked frequently while the dose is being adjusted. Your team will also decide how to monitor liver and kidney function, thyroid health, mood and other concerns. Tell them about changes even if you are unsure whether the medicine caused them.

Pregnancy needs a specific discussion. BESREMi can harm an unborn baby. Talk with your hematologist before pregnancy or breastfeeding; do not assume that general advice about interferon applies to every interferon product.

Should you consider switching to BESREMi?

Start with the reason you might change. Are counts difficult to control? Are side effects interfering with daily life? Have your treatment goals changed?

Approval does not mean every adult with ET needs BESREMi. Some people do not need medicine to lower blood counts, known as cytoreductive therapy. Others are doing well on their current treatment. Your history of clots or bleeding, symptoms, blood counts, mutation status and other health conditions all help guide the discussion.

Questions to bring to your MPN specialist

1. Do I need medicine to lower my blood counts now, and what are we trying to achieve beyond the platelet number?
2. What specific benefit might BESREMi offer me compared with staying on my current treatment?
3. How closely do I match the patients studied, given my mutation, risk level and treatment history?
4. If we switch, how will we manage the transition, and which of my current medicines should continue?
5. What will we measure to judge whether treatment is helping, and when will we reassess?
6. Which side effects should prompt a same-day call, and which require emergency care?
7. What monitoring and injection training will I need, and who should I contact between visits?
8. What will I pay after insurance, and what is our plan if coverage is delayed?

If you need help finding someone with MPN experience, our MPN Specialist Directory is a starting point.

Availability, insurance and financial support

PharmaEssentia announced that BESREMi for ET would be available in the United States immediately after approval. Starting treatment can still take time because of insurance authorization and specialty-pharmacy arrangements.

PharmaEssentia SOURCE offers help understanding coverage and possible financial assistance. Patients can call 800-700-5053, Monday through Friday, 8 a.m. to 8 p.m. Eastern Time.

Assistance depends on eligibility. Commercial-insurance copay programs generally exclude Medicare and Medicaid. If you have government insurance, ask about other resources rather than assuming a copay offer applies to you. Get an estimate of your own cost before treatment starts.

BESREMi for ET: common questions

Is BESREMi FDA approved for essential thrombocythemia?

Yes. BESREMi was approved on August 31, 2026, for adults with ET. Its generic name is ropeginterferon alfa-2b-njft.

Do I have to try hydroxyurea first?

The approved indication does not require it. The main randomized study did enroll patients who had already tried hydroxyurea, so discuss how that evidence applies to your situation. Insurance requirements may differ from the approved indication.

Is BESREMi chemotherapy?

BESREMi is an interferon-based biologic medicine, rather than conventional chemotherapy. That distinction does not mean it is free of significant side effects.

Does my JAK2, CALR or MPL mutation determine eligibility?

The approval is not restricted to a particular mutation. Your mutation profile still helps your specialist assess risk and interpret the research. EXCEED-ET reported molecular responses across these three driver mutations, with differing response rates.

Can BESREMi cure ET or let me stop treatment?

BESREMi is not a cure. An improvement in blood counts or mutation burden does not automatically mean treatment can stop. Any change requires an individual plan with your hematologist.

What this means for your next appointment

BESREMi for essential thrombocythemia adds an approved option with evidence for blood-count control and reductions in mutation burden. Ask your specialist what improvement would make a treatment change worthwhile for you.

References

1. US Food and Drug Administration. FDA Approves Treatment for Essential Thrombocythemia. Accessed September 13, 2026.
2. PharmaEssentia. BESREMi US Prescribing Information and Medication Guide. Revised August 2026. Linked in the safety section above.
3. Mesa R, Gill H, Zhang L, et al. SURPASS-ET phase 3 trial. The Lancet Haematology. 2025;12:e862–e875. DOI: 10.1016/S2352-3026(25)00264-9.
4. Reeves BN, El Chaer F, Foltz L, et al. Ropeginterferon alfa-2b-njft treatment in essential thrombocythemia across different driver mutations: EXCEED-ET. The Lancet Regional Health – Americas. 2026;61:101529. Published online June 10, 2026. DOI: 10.1016/j.lana.2026.101529.
5. Conroy R. How Will Ropeginterferon Alfa’s Approval Affect Essential Thrombocythemia? CancerNetwork. September 7, 2026. Interview with Ruben Mesa, MD.
6. PharmaEssentia. SOHO 2026 meeting announcement. September 9, 2026. Summarizes SURPASS-ET extension poster MPN-944 and community oncology poster MPN-1090; partial two-year results previously presented at EHA 2026.
7. Mesa RA. Ropeginterferon Alfa-2b FDA Approval Marks an Important First Step in ET. Blood Cancers Today. September 11, 2026. Expert interview.
8. PharmaEssentia. FDA approval announcement. August 31, 2026. Business Wire.
9. PharmaEssentia SOURCE. Patient support and financial assistance information. Accessed September 13, 2026. Linked in the access section above.

About the Author

David Wallace is a nationally recognized myeloproliferative neoplasm (MPN) patient advocate, writer, and the founder and publisher of PV Reporter. He also founded MPN Cancer Connection, a 501(c)(3) nonprofit organization, and serves as its executive director. Diagnosed with polycythemia vera in 2009 and now in complete molecular remission, David has spent more than a decade helping patients understand MPN research, treatment options, and the questions to ask their healthcare teams. His work brings the patient voice into discussions with clinicians, researchers, and industry leaders.

Medical Disclaimer

This article is for educational purposes only and is not medical advice. It does not replace consultation with a qualified hematologist or MPN specialist. Discuss all diagnosis and treatment decisions with your healthcare team.