Assessment of flonoltinib maleate versus ruxolitinib phosphate in intermediate- to high-risk myelofibrosis (FMF-02): study protocol for a multicenter, randomized, open-label phase IIB trial

Background: Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, splenomegaly, debilitating constitutional symptoms, and cytopenias. Despite the benefits of ruxolitinib in controlling symptoms and spleen volume, challenges such as myelosuppression and limited impact on underlying fibrosis persist, particularly in cytopenic patients. Flonoltinib maleate (FM), a novel JAK2/FLT3/CDK6 inhibitor, shows preliminary potential in improving hematologic parameters and reducing fibrosis. Objectives: To evaluate the efficacy of low-/high-dose FM compared with RUX (primary objective), along with safety and the pharmacokinetic profile of FM (secondary objectives), in patients with intermediate- to high-risk MF (Trial registration: NCT06457425). Design: FMF-02 is a multicenter, randomized, open-label, active-controlled, phase IIb clinical trial. Methods: Approximately 75 adults with primary or secondary MF will be randomized in a 1:1:1 ratio to receive low-dose FM (50 mg once daily), high-dose FM (100 mg once daily), or RUX (5, 15, or 20 mg twice daily, based on platelet count), with randomization stratified by the Dynamic International Prognostic Scoring System risk category. The primary endpoint is the proportion of patients achieving ⩾35% spleen volume reduction (SVR35) at week 24, as assessed by a blinded Independent Review Committee. Key secondary endpoints include the proportion with ⩾50% reduction in Total Symptom Score (TSS50), changes in myelofibrosis grade, objective remission rate International Working Group for Myelofibrosis Research and Treatment (IWG-MRT) criteria, and safety. Subjects in the RUX group who complete the 24-week treatment or experience disease progression due to splenomegaly will crossover to receive FM. All subjects will continue long-term therapy until meeting discontinuation criteria, followed by survival follow-up. Results: The study commenced in June 2024 and is currently ongoing. The results will provide comparative data on the efficacy and safety profiles of FM versus RUX, including analyses of spleen response, symptom burden, hematologic parameters, and bone marrow fibrosis. Conclusion: The FMF-02 trial is the first randomized phase IIb study directly comparing the novel inhibitor FM against RUX. Its findings are expected to generate pivotal evidence regarding whether FM offers superior or differentiated clinical benefits, thereby informing its potential as a frontline therapy for intermediate- to high-risk MF and guiding the design of future phase III studies.