Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S390 decreased from 1450/mL to 630/mL over the first 4 weeks of study. Conclusion: In MF patients with elevated PBBs, blasts declined over time among pacritinib-treated patients across two clinical trials. Further studies are warranted to assess the efficacy of pacritinib, either alone or in combination with other agents, for treatment of accelerated or blast phase MF. Keywords: MPN, myelofibrosis, MF, blasts, pacritinib, clinical MPN-346 INDEPENDENCE: Enrolling Phase III Trial to Study the Efficacy and Safety of Luspatercept versus Placebo in Patients With Myelofibrosis on JAK2 Inhibitor (JAK2i) Therapy Requiring Red Blood Cell Transfusions (RBCTs) Jean-Jacques Kiladjian MD, PhD1, Claire Harrison MD2, Ruben A. Mesa MD3, Haifa K. Al-Ali MD4, John Mascarenhas MD5, Fabian Sanabria MD6, Julie Vienne Bürki PhD6, Bourras-Rezki Bengoudifa MS6, Francesco Passamonti MD7 1Hôpital Saint-Louis et Université Paris Diderot, Paris, France. 2Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom. 3Atrium Health Wake Forest Baptist Comprehensive Cancer Center, Winston-Salem, USA. 4Universitätsklinikum Halle (Saale), Halle, Germany. 5Icahn School of Medicine, Mount Sinai, USA. 6Bristol Myers Squibb, Boudry, Switzerland. 7Università di Milano Statale, Policlinico di Milano, Ospedale Maggiore, Fondazione I.R.C.C.S. Ca Granda, Milano, Italy Context: Many patients with myelofibrosis develop anemia and RBCT dependence, associated with poor prognosis. Luspatercept is a first-in-class erythroid maturation agent approved for treatment of anemia in specific RBCT-dependent patients with b-thalassemia/ myelodysplastic syndromes. In a phase II trial (NCT03194542), 26.3% of RBCT-dependent, ruxolitinib-treated patients with myelofibrosis achieved ≥12 weeks of RBCT independence (RBCTI) with luspatercept (Gerds AT, et al. American Society Clinical Oncology 2023; Poster 7016). Objective: INDEPENDENCE (NCT04717414) is a Phase III, double-blind trial to determine the efficacy of luspatercept versus placebo for treatment of anemia in patients with MPN-associated myelofibrosis on concomitant JAK2i therapy requiring RBCT. Design: Eligible patients (aged ≥18 years; requiring 4-12 RBC units/12 weeks; ≥32 weeks concomitant JAK2i therapy /≥16 weeks stable daily dose; no anemia from other causes or medications with hematopoietic effects ≤8 weeks before randomization) will be randomized 2:1 to luspatercept (starting at 1.33 mg/kg; titration up to 1.75 mg/kg) subcutaneously, or placebo, every 3 weeks. Stratification factors include baseline RBCT and DIPSS score. Treatment phase: 24-week core period and disease response assessment (Day 169). Best supportive care is allowed. Clinical benefit (CB): RBC-TI for any consecutive ≥12-week period in weeks 1–24, RBCT burden reduction by ≥50% and by ≥4 RBC units for ≥12 weeks in weeks 1–24, or incomplete response duration (RBC-TI for ≥4 weeks immediately up to end of Week 24). Patients with CB can continue luspatercept until loss of benefit, progression to acute myelogenous leukemia, unacceptable toxicity, consent withdrawal, or meeting other discontinuation criteria. Patients without CB (Day 169) can be unblinded and those on placebo can cross over to open-label luspatercept. Planned post-treatment follow-up period: 5-years post-first dose or 3 years post-last dose. As of May 10, 2023, 53% (164/309) of planned patients have been enrolled globally across 21 countries and 150 activated sites. Main Outcome Measure: Primary endpoint: proportion of patients who become RBCT-free over any consecutive 12-week period starting between randomization and Week 24. Previous Presentation: MPN (International congress on Myeloproliferative Neoplasm) 2022 (P116) and DGHO (Deutschen, Österreichischen und Schweizerischen Gesellschaften für Hämatologie und Medizinische Onkologie) 2022 (P911). Funding: Bristol Myers Squibb Keywords: MPN, myelofibrosis, anemia, luspatercept MPN-361 Ropeginterferon Alfa‑2b for Young High‑Risk Patients With Essential Thrombocythemia ‑ Evaluation of Clinicohematologic Response and Safety Profile: Single‑Center Experience Marija Popova-Labachevska MD University Clinic for Hematology, Skopje, Macedonia, the former Yugoslav Republic of Context: Interferon’s ability to induce not only hematologic but also molecular response in patients with BCR-ABL–negative myeloproliferative neoplasms (MPNs) has already been established. Ropeginterferon alfa-2b has emerged as an important therapeutic tool, currently approved only for treatment of patients with polycythemia vera (PV). Objective: Here we present our experience with ropeginterferon alfa-2b in 16 young patients with BCR-ABL– negative MPNs, diagnosed and treated at the University Clinic for Haematology in Skopje, R. of North Macedonia. Design: In this retrospective observational study, we tested the efficiency of ropeginterferon alfa-2b in MPNs focusing on clinicohematologic response and safety profile. Patients: 16 patients were included. Responses were evaluated by European LeukemiaNet, International Working Group Myeloproliferative Neoplasms Research and Treatment and European Myelofibrosis Network standardized criteria sets and occurrence of side effects was recorded. Results: In our cohort, 11 patients were female (69%), with average age at diagnosis of 36 years (17-51); Twelve patients had essential thrombocythemia (ET), one PV and three patients had hypercellular phase of primary myelofibrosis (PMF); JAK2V617F mutation was detected in 10 (62.5%), CALR mutation in three (19%), and three patients were triple-negative (19%). We used the revised International Prognostic Score for Thrombosis in Essential Thrombocythemia score to define high-risk patients. Bone marrow biopsy before treatment initiation was performed in all patients in order to categorize the grade of fibrosis. Splenomegaly was present in four (25%) while three patients underwent splenectomy because of splenic vein thrombosis. In seven pts (43.7%) ropeginterferon alfa-2b was used as first-
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