A Phase 3 Study of Pelabresib (DAK539) and Ruxolitinib in Myelofibrosis (MF)

Key Inclusion Criteria: * Participants have diagnosis of primary myelofibrosis (PMF) or post-polycythemia vera myelofibrosis (post-PV MF) or post-essential thrombocythemia myelofibrosis (post-ET MF) according to the International Consensus Classification (ICC) of Myeloid Neoplasms and Acute Leukemias 2022 * DIPSS risk category of intermediate-1, intermediate-2 or high-risk * Spleen volume ≥ 450 cm3 by CT or MRI scan (local read sufficient if no central read available) * Have an average TSS of ≥15 within 7 days prior to randomization, using MFSAF v. 4.0 (at least 4 out of 7 TSS assessments required for average calculation) * Participants with an Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1, or 2 * Blasts \<5% in peripheral blood. Assessment of blasts in peripheral blood is mandatory at screening * Platelet count ≥ 100 x 10\^9/L in the absence of growth factors or transfusions for the previous 4 weeks Key Exclusion Criteria: * Prior splenectomy at any time or splenic irradiation in the previous 6 months * Prior hematopoietic cell transplant or participant anticipated to receive a hematopoietic cell transplant within 24 weeks from the date of randomization * Blasts ≥ 5% in bone marrow if results available at screening or history of accelerated phase (AP) or leukemic transformation * History of a malignancy (other than MF, PPV-MF or PET-MF) in the past 3 years in need of systemic treatment * Received any approved or investigational agent other than hydroxyurea or anagrelide for the treatment of MF within 14 days of first dose of study treatment or within 5 half-lives of the approved or investigational agent, whichever is longer * Prior treatment with any JAK inhibitor or Bromodomain and extraterminal domain (BET) inhibitor Other protocol-defined inclusion/exclusion criteria may apply.