Here is the design of a clinical trial:

Official Title: A Phase 1/3 Study to Evaluate Efficacy and Safety of Selinexor, a Selective Inhibitor of Nuclear Export, in Combination with Ruxolitinib in Treatment-naïve Patients with Myelofibrosis

Included conditions:
- Myelofibrosis

Study Armgroups:
- {'label': 'Phase 1a: Cohort 1: Selinexor 40 mg + Ruxolitinib BID', 'type': 'EXPERIMENTAL', 'description': 'Participants with MF will receive a dose of 40 milligrams (mg) selinexor oral tablets once weekly (QW) on Days 1, 8, 15, and 22 of each 28-day cycle in combination with 15 or 20 mg ruxolitinib twice a day (BID) based on the participants baseline platelet count.', 'interventionNames': ['Drug: Selinexor', 'Drug: Ruxolitinib']}
- {'label': 'Phase 1a: Cohort 2: Selinexor 60 mg + Ruxolitinib BID', 'type': 'EXPERIMENTAL', 'description': 'Participants with MF will receive a dose of 60 mg selinexor oral tablets QW on Days 1, 8, 15, and 22 of each 28-day cycle in combination with 15 or 20 mg ruxolitinib BID based on the participants baseline platelet count.', 'interventionNames': ['Drug: Selinexor', 'Drug: Ruxolitinib']}
- {'label': 'Phase 1b: Selinexor and Ruxolitinib BID', 'type': 'EXPERIMENTAL', 'description': 'Participants with MF will receive a dose of 40 or 60 mg selinexor oral tablets QW on Days 1, 8, 15, and 22 of each 28-day cycle in combination with 15 or 20 mg ruxolitinib BID based on the participants baseline platelet count.', 'interventionNames': ['Drug: Selinexor', 'Drug: Ruxolitinib']}
- {'label': 'Phase 3: Selinexor 60 mg + Ruxolitinib BID', 'type': 'EXPERIMENTAL', 'description': 'Participants with MF will receive a fixed starting dose of 60 mg selinexor (RD) oral tablets QW on Days 1, 8, 15, and 22 of each 28-day cycle in combination with a starting dose of 15 or 20 mg ruxolitinib BID based on the participants baseline platelet count.', 'interventionNames': ['Drug: Selinexor', 'Drug: Ruxolitinib']}
- {'label': 'Phase 3: Placebo + Ruxolitinib BID', 'type': 'ACTIVE_COMPARATOR', 'description': 'Participants with MF will receive a matching placebo of selinexor oral tablets QW on Days 1, 8, 15, and 22 of each 28-day cycle in combination with a starting dose of 15 or 20 mg ruxolitinib BID based on the participants baseline platelet count.', 'interventionNames': ['Other: Placebo', 'Drug: Ruxolitinib']}

Interventions:
- {'type': 'DRUG', 'name': 'Selinexor', 'description': 'Participants will receive a dose of 40 or 60 mg selinexor oral tablets QW.', 'armGroupLabels': ['Phase 1a: Cohort 1: Selinexor 40 mg + Ruxolitinib BID', 'Phase 1a: Cohort 2: Selinexor 60 mg + Ruxolitinib BID', 'Phase 1b: Selinexor and Ruxolitinib BID'], 'otherNames': ['KPT-330']}
- {'type': 'DRUG', 'name': 'Selinexor', 'description': 'Participants will receive a dose of 60 mg selinexor oral tablets QW.', 'armGroupLabels': ['Phase 3: Selinexor 60 mg + Ruxolitinib BID'], 'otherNames': ['KPT-330']}
- {'type': 'OTHER', 'name': 'Placebo', 'description': 'Participants will receive a matching placebo of selinexor oral tablets QW', 'armGroupLabels': ['Phase 3: Placebo + Ruxolitinib BID']}
- {'type': 'DRUG', 'name': 'Ruxolitinib', 'description': 'Participants will receive a dose of 15 or 20 mg ruxolitinib oral tablets BID.', 'armGroupLabels': ['Phase 1a: Cohort 1: Selinexor 40 mg + Ruxolitinib BID', 'Phase 1a: Cohort 2: Selinexor 60 mg + Ruxolitinib BID', 'Phase 1b: Selinexor and Ruxolitinib BID', 'Phase 3: Placebo + Ruxolitinib BID', 'Phase 3: Selinexor 60 mg + Ruxolitinib BID']}

Primary Outcomes:
- {'measure': 'Phase 3: Proportion of Participants with Spleen Volume Reduction (SVR) of Greater than or Equal to (>=) 35 Percent (%) (SVR35) at Week 24 Measured by the Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) Scan', 'timeFrame': 'At Week 24'}
- {'measure': 'Phase 3: Absolute mean change in TSS (Abs-TSS) from baseline to Week 24 as measured by the Myelofibrosis Symptom Assessment Form (MFSAF) v4.0', 'timeFrame': 'At Week 24'}
- {'measure': 'Phase 1: Maximum Tolerated Dose (MTD)', 'timeFrame': 'Approximately within the first cycle (28 days) of therapy'}
- {'measure': 'Phase 1: Recommended Phase 2 Dose (RP2D)', 'timeFrame': 'Approximately within the first cycle (28 days) of therapy'}
- {'measure': 'Phase 1: Number of Participants With Adverse Events (AEs) by Occurrence, Nature, and Severity', 'timeFrame': 'From start of drug administration up to 30 days after last dose of study treatment (approximately 48 months)'}

Please estimate the sample size based on the assumption: 
80% power, 1-sided type 1 error of 0.025
2.4.
        Sample size
        To provide 80% power for statistical significance of the co-primary endpoints at the overall 1-sided type 1 error of 0.025 level, approximately 350 patients will be enrolled.