To Evaluate the Efficacy and Safety of Parsaclisib and Ruxolitinib in Participants With Myelofibrosis (LIMBER-313)

This is a Phase 3, randomized, double-blind study of the combination of the PI3Kδ inhibitor parsaclisib or matching placebo and the JAK1/2 inhibitor ruxolitinib in participants with PMF or secondary MF (PPV-MF or PET-MF) with DIPSS risk category of intermediate or high. Prospective participants must have not received prior MF therapy with a JAK inhibitor or a PI3K inhibitor. After participants have been determined to be eligible for the study and completed the baseline symptom diary assessment for 7 days, they will be randomized to 1 of 2 treatment groups, with stratification for platelet count (≥ 100 × 10\^9/L vs 50 to \< 100 × 10\^9/L inclusive) and DIPSS risk category (high vs intermediate-2 vs intermediate-1). Once all enrolled participants completed the week 24 assessments the study will be unblinded and and participants randomized to placebo will have the opportunity to cross over to begin receiving parsaclisib, together with continued ruxolitinib, as long as hematology parameters are adequate.