ruxolitinib will be administered BID orally

placebo will be administered QD orally

Symptoms of myelofibrosis were assessed using the MFSAF v4.0 diary. The MFSAF v4.0 is composed of 7 individual symptom scores (fatigue, night sweats, itchiness, abdominal discomfort, pain under left ribs, early satiety, bone pain), each collected daily using a 0- (no symptoms) to 10-point (worst imaginable symptoms) scale. The daily TSS (0 to 70) is the sum of the 7 individual symptom scores collected on the same day. Higher TSS indicate more severe symptoms. The TSS was missing if there were any missing individual scores. Observations with missing dates were excluded from the analysis. The Baseline/Week 24 total score was defined as the average of the daily total scores from the last 7 days before the first dose of parsaclisib, placebo, or ruxolitinib/the Week 24 visit. The Baseline/Week 24 total scores was missing if there were ≥4 missing out of the 7 daily total scores. Change from Baseline was calculated as the post-Baseline value minus the Baseline value.

Symptoms of myelofibrosis were assessed using the MFSAF v4.0 diary. The MFSAF v4.0 is composed of 7 individual symptom scores (fatigue, night sweats, itchiness, abdominal discomfort, pain under left ribs, early satiety, bone pain), each collected daily using a 0- (no symptoms) to 10-point (worst imaginable symptoms) scale. The daily TSS (0 to 70) is the sum of the 7 individual symptom scores collected on the same day. Higher TSS indicate more severe symptoms. The TSS was missing if there were any missing individual scores. Observations with missing dates were excluded from the analysis. The Baseline/Week 24 total score was defined as the average of the daily total scores from the last 7 days before the first dose of parsaclisib, placebo, or ruxolitinib/the Week 24 visit. The Baseline/Week 24 total scores was missing if there were ≥4 missing out of the 7 daily total scores.

Overall survival was defined as the interval between the randomization date and the date of death due to any cause.

An adverse event (AE) is defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not it is considered drug related. An AE could therefore be any unfavorable or unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of study treatment. A TEAE is defined as any AE either reported for the first time or the worsening of a pre-existing event after the first dose of study drug until 30 to 35 days after the last dose of parsaclisib/matching placebo or ruxolitinib.

An AE is defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not it is considered drug related. A TEAE is defined as any AE either reported for the first time or the worsening of a pre-existing event after the first dose of study drug until 30 to 35 days after the last dose of parsaclisib/matching placebo or ruxolitinib. The severity of AEs was assessed using Common Terminology Criteria for Adverse Events (CTCAE) v5.0 Grades 1 through 5. Grade 1: mild; asymptomatic or mild symptoms; clinical or diagnostic observations only; intervention not indicated. Grade 2: moderate; minimal, local or noninvasive intervention indicated; limiting instrumental activities of daily living (ADL). Grade 3: severe or medically significant but not immediately life-threatening; hospitalization or prolongation of hospitalization indicated; disabling; limiting self care ADL. Grade 4: life-threatening urgent intervention indicated. Grade 5: death related to AE.

The time to the first ≥35% reduction in spleen volume is defined as the time from randomization to the first time participants had ≥35% reduction in spleen volume.

The duration of ≥35% reduction from Baseline in spleen volume was defined as the interval between the first spleen volume measurement that was a ≥35% reduction from Baseline and the date of the first measurement that was no longer a ≥35% reduction from Baseline.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.

Participants were randomized to receive placebo plus ruxolitinib beginning on Day 1 and continued on this regimen until they left the study. Participants with a Baseline platelet count ≥100 × 10^9/Liter received ruxolitinib 15 mg BID. Participants with a Baseline platelet count of 50 to < 100 × 10^9/Liters inclusive received ruxolitinib 5 mg BID. Participants were also stratified according to the DIPSS risk category (high versus intermediate-2 versus intermediate-1). Participants received matching placebo at a dose of 5 mg QD. After 24 weeks, participants randomized to receive placebo plus ruxolitinib could have switched to treatment with parsaclisib plus ruxolitinib per the regimen received during the first 24 weeks of the study. Treatment continued for as long as the regimen was tolerated and the participant did not meet any discontinuation criteria.