• Primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF (as defined by Tefferi and Vardiman 2008

• Platelet count of \<50,000/μL at Screening (Day -35 to Day -3)

• Dynamic International Prognostic Scoring System Intermediate-1, Intermediate-2, or High-Risk (Passamonti et al 2010

• Palpable splenomegaly ≥5 cm below the lower costal margin (LCM) in the midclavicular line as assessed by physical examination

• TSS of ≥10 on the MPN-SAF TSS 2.0 or a single symptom score of ≥5 or two symptoms of ≥3, including only the symptoms of left upper quadrant pain, bone pain, itching, or night sweats.The TSS criteria need only to be met on a single day.

• Age ≥18 years

• Eastern Cooperative Oncology Group performance status 0 to 2

• Peripheral blast count of \<10% throughout the Screening period prior to randomization

• Absolute neutrophil count of ≥500/µL

⁃ Left ventricular cardiac ejection fraction of ≥50% by echocardiogram or multigated acquisition scan

⁃ Adequate liver and renal function, defined by liver transaminases (aspartate aminotransferase \[AST\]/serum glutamic-oxaloacetic transaminase \[SGOT\] and alanine aminotransferase \[ALT\]/serum glutamic pyruvic transaminase \[SGPT\]) ≤3 × the upper limit of normal (ULN) (AST/ALT ≤5 × ULN if transaminase elevation is related to MF), total bilirubin ≤4 x ULN (in cases where total bilirubin is elevated, direct bilirubin ≤4 × ULN, is required) and creatinine ≤2.5 mg/dL

⁃ Adequate coagulation defined by prothrombin time/international normalized ratio and partial thromboplastin time ≤1.5 × ULN

⁃ If fertile, willing to use highly effective birth control methods during the study

⁃ Willing to undergo and able to tolerate frequent MRI or CT scan assessments during the study

⁃ Able to understand and willing to complete symptom assessments using a patient-reported outcome instrument

⁃ Provision of signed informed consent