Ropeginterferon alfa-2b in hydroxyurea-intolerant or hydroxyurea-refractory essential thrombocythaemia (SURPASS ET): a multicentre, open-label, randomised, active-controlled, phase 3 study

Background The initial therapy for high-risk essential thrombocythaemia is usually hydroxyurea, but about a third of patients develop intolerance or resistance. A standard second-line agent has been anagrelide. Ropeginterferon alfa-2b, a new-generation interferon-based therapy, is approved for polycythaemia vera. We aimed to assess efficacy and safety of ropeginterferon alfa-2b compared with anagrelide in patients with essential thrombocythaemia with leukocytosis who are intolerant or resistant to hydroxyurea. Methods The SURPASS ET open-label, randomised, active-controlled, phase 3 trial was done at 55 clinical sites across China, Japan, Taiwan, Hong Kong, South Korea, the USA, Singapore, and Canada and enrolled patients aged 18 years and older with high-risk (age >60 years with JAK2 Val617Phe or a history of disease-related thrombosis or haemorrhage), hydroxyurea-intolerant or hydroxyurea-resistant essential thrombocythaemia and white blood cell (WBC) count greater than 10 × 10⁹ cells/L. Patients were randomly assigned (1:1) to ropeginterferon alfa-2b or anagrelide, stratified by platelet count, symptom score, and country. Ropeginterferon alfa-2b was subcutaneously dosed every 2 weeks, initially at 250 μg, then titrated to 350 μg at week 2, and to 500 μg from week 4 onward. Anagrelide was orally dosed according to the US Food and Drug Administration-approved prescribing information. The primary endpoint was the rate of response at months 9 and 12, as per modified European LeukemiaNet (ELN) criteria. The main planned analysis for the study was done in the intention-to-treat population. The trial is registered at ClinicalTrials.gov, NCT04285086 and is completed, and an extension study for collecting long-term data is ongoing. Findings Between Aug 25, 2020, and Nov 12, 2024, 245 patients were screened and 174 were randomly assigned (91 to ropeginterferon alfa-2b and 83 to anagrelide). The median follow-up was 12·5 months (IQR 11·5–12·9). At baseline, 47 (52%) of 91 participants in the ropeginterferon alfa-2b group and 44 (53%) of 83 participants in the anagrelide group were female. 167 (96%) of 174 participants were Asian and seven (4%) were White. The trial met its primary endpoint, with 39 (43%) of 91 participants in the ropeginterferon alfa-2b group showing durable modified ELN criteria responses at months 9 and 12, compared with five (6%) of 83 participants in the anagrelide group. This difference (36·5%, 95% CI 25·4–47·7) was significant (p=0·0001). Grade 3 or worse treatment-emergent adverse events occurred in 27 (34%) of 80 patients in the anagrelide group and 21 (23%) of 91 patients in the ropeginterferon alfa-2b group. In the ropeginterferon alfa-2b group, the most common grade 3 or worse adverse events were infections and infestations, occurring eight (9%) of 91 patients, compared with five (6%) of 80 patients in the anagrelide group. In the anagrelide group, the most frequent grade 3 or worse adverse events were nervous system disorders, occurring in six (8%) of 80 patients, compared with one (1%) of 91 patients with ropeginterferon alfa-2b. Serious adverse events occurred in 24 (30%) of 80 participants in the anagrelide group and 13 (14%) of 91 participants in the ropeginterferon alfa-2b group). The most common serious adverse event was cerebral infarction, which occurred in four (5%) of 80 patients in the anagrelide group but was not observed in the ropeginterferon alfa-2b group. There were no treatment-related deaths in either study group. Interpretation Our findings suggest that ropeginterferon alfa-2b could be considered as a second-line treatment option for patients with essential thrombocythaemia and leukocytosis. Funding PharmaEssentia.