The First New Treatment for Essential Thrombocythemia in Nearly 30 Years

The treatment landscape of essential thrombocythemia (ET) has changed little for decades.

That changed in August 2026, when the U.S. Food and Drug Administration (FDA) approved ropeginterferon alfa-2b-njft (Besremi) for the treatment of adults with essential thrombocythemia.

The approval introduces a long-acting interferon formulation into the U.S. treatment landscape for ET and expands the role of ropeginterferon beyond its previous FDA indication in polycythemia vera.

Why Is This Approval Important?

Essential thrombocythemia is a chronic myeloproliferative neoplasm characterized by clonal hematopoiesis and persistent thrombocytosis.

Although platelet elevation is a defining feature, the clinical burden of ET is determined not only by the platelet count but also by thrombotic and hemorrhagic complications, symptoms, splenomegaly and, in some patients, disease progression.

Current management has traditionally focused on reducing thrombotic risk and controlling blood counts.

Treatment options have included antiplatelet therapy and cytoreductive agents such as hydroxyurea, anagrelide and interferon-based therapy.

The 2026 FDA approval is notable because it provides a new approved cytoreductive option for adults with ET after decades without a newly approved treatment specifically for the disease.

From Polycythemia Vera to Essential Thrombocythemia

Ropeginterferon alfa-2b is not a completely new drug.

The FDA originally approved Besremi in 2021 for adults with polycythemia vera. Its 2026 approval expands the indication to essential thrombocythemia, another classic Philadelphia chromosome-negative myeloproliferative neoplasm.

Ropeginterferon is a long-acting interferon alfa formulation administered subcutaneously. Unlike agents that primarily suppress blood-cell production through conventional cytoreduction, interferon-based therapy has attracted particular interest because of its effects on abnormal hematopoietic cells and its potential to reduce the burden of the malignant clone.

How Does Ropeginterferon Work?

Ropeginterferon alfa-2b is a long-acting, mono-PEGylated form of recombinant interferon alfa-2b. Type I interferons exert their effects by binding to interferon receptors on the surface of cells and activating intracellular signaling pathways that alter the expression of multiple genes.

In essential thrombocythemia, this mechanism is relevant because interferon can act on hematopoietic cells within the abnormal myeloproliferative clone. Interferon has antiproliferative and immunomodulatory effects and may reduce the burden of the abnormal clone rather than simply suppressing platelet production.

ET is commonly driven by mutations involving JAK2, CALR or MPL, which contribute to abnormal signaling and proliferation of hematopoietic cells. Ropeginterferon does not directly inhibit these driver mutations in the way a selective kinase inhibitor would.

Instead, its effects on hematopoietic cells may result in reductions in the burden of these mutant clones.

Recent data from the phase 2b EXCEED-ET study provide additional evidence for this potential disease-modifying effect.

At Month 13, molecular responses were observed among patients with JAK2V617F, CALR and MPL driver mutations, although the clinical significance of molecular responses and their relationship to long-term outcomes remain under investigation.

This potential effect on the underlying clone is one of the reasons interferon-based therapy has attracted interest in myeloproliferative neoplasms.

What Did the SURPASS-ET Trial Show?

The FDA approval was supported by the SURPASS-ET study, an open-label, multicenter, randomized trial comparing ropeginterferon alfa-2b with anagrelide in adults with essential thrombocythemia who had an inadequate response or intolerance to hydroxyurea.

The study enrolled 174 patients: 91 received ropeginterferon and 83 received anagrelide.

The primary efficacy assessment was based on a durable modified European LeukemiaNet response at Months 9 and 12. The response required control of blood counts, improvement or non-progression of splenomegaly, and absence of bleeding or thrombotic events.

The results showed a substantial difference between the treatment groups:

• 37.4% achieved the defined durable response with ropeginterferon
• 3.6% achieved the response with anagrelide

The difference was observed at both Month 9 and Month 12.

How Will Besremi Be Given?

For adults with ET, the FDA-recommended starting dose is 250 mcg subcutaneously, followed by 350 mcg at Week 2 and 500 mcg at Week 4. The maintenance dose is 500 mcg every two weeks unless dose modification is required for tolerability.

This every-two-week administration is an important practical feature of ropeginterferon and distinguishes it from daily oral cytoreductive therapy.

Safety Considerations

The benefits of interferon therapy must be considered alongside its safety profile.

In the FDA’s assessment of Besremi in ET, commonly reported adverse reactions included transaminase elevations, anemia, fever, bacterial infection, pruritus and weight loss.

The prescribing information also carries a boxed warning concerning serious disorders associated with interferon alfa products, including potentially severe neuropsychiatric, autoimmune, ischemic and infectious disorders.

These considerations make patient selection and monitoring important when deciding where ropeginterferon fits into ET management.

What Could This Mean for ET Treatment?

The significance of the approval goes beyond the addition of another cytoreductive drug.

Modern MPN biology increasingly focuses on the underlying clonal architecture of disease. JAK2, CALR and MPL mutations drive signaling abnormalities, while additional molecular changes and inflammatory mechanisms contribute to disease evolution and complications.

This has shifted interest toward therapies that may do more than simply normalize blood counts.

Interferon-based treatment is particularly relevant to this discussion because it has demonstrated molecular and disease-modifying potential in MPNs, although the clinical meaning and durability of such responses continue to be studied.

The recent NEJM review notes that current MPN therapies generally focus on symptoms, thrombosis and splenomegaly, while pegylated interferon alfa and JAK2 inhibitors have shown disease-modifying effects in some patients.

A New Chapter for Essential Thrombocythemia

The FDA approval of ropeginterferon alfa-2b marks an important change in the therapeutic landscape of essential thrombocythemia.

For patients with inadequate response or intolerance to hydroxyurea, the SURPASS-ET results provide clinical evidence supporting ropeginterferon as an additional cytoreductive option.

The magnitude of the difference in durable response compared with anagrelide makes the approval particularly notable.

At the same time, the approval does not resolve all questions surrounding ET treatment. The optimal sequencing of cytoreductive therapies, patient selection, long-term molecular responses and the impact of treatment on thrombosis, progression and survival will remain important areas of investigation.

What makes the 2026 approval especially significant is that it brings a new therapeutic approach to a disease whose treatment options had changed relatively little for decades.

Ropeginterferon may therefore represent not simply another way to lower the platelet count, but another step toward treating essential thrombocythemia as a molecularly defined clonal disease.

FAQ

1. Why is the FDA approval important?

Besremi is the first new FDA-approved treatment for ET in nearly 30 years, expanding options for adults with the disease.

2. How does Besremi work?

It is a long-acting interferon that may suppress abnormal blood-cell production and reduce the malignant clone.

3. How effective was it?

In SURPASS-ET, 37.4% of patients achieved a durable response with Besremi, compared with 3.6% receiving anagrelide.

4. How is it administered?

Besremi is injected under the skin, with maintenance dosing generally every two weeks.

5. What are the key safety concerns?

Important risks include liver-enzyme elevations, anemia, fever, infection, pruritus, weight loss and serious neuropsychiatric or autoimmune complications.

Written by Hermine Sayiyan, MD