Efficacy of Momelotinib Versus Best Available Therapy in Anemic or Thrombocytopenic Subjects With Primary Myelofibrosis (MF), Post-polycythemia Vera MF, or Post-essential Thrombocythemia MF

Key Inclusion Criteria:

Palpable splenomegaly at least 5 cm below left costal margin
Confirmed diagnosis of PMF in accordance, or Post-PV/ET MF

Currently or previously treated with ruxolitinib for PMF or Post-PV/ET MF for at least 28 days, and characterized by

Requirement for RBC transfusion while on ruxolitinib treatment, OR

Dose adjustment of ruxolitinib to < 20 mg twice daily at start of or during ruxolitinib treatment AND at least one of the following while on ruxolitinib treatment:

≥ Common Terminology Criteria for Adverse Events (CTCAE) Grade 3 thrombocytopenia, OR
≥ CTCAE Grade 3 anemia, OR
≥ CTCAE Grade 3 hematoma (bleed)
High risk OR intermediate-2 risk as defined by Dynamic International Prognostic Scoring System (DIPSS), OR intermediate-1 risk as defined by DIPSS and associated with symptomatic splenomegaly, and/or hepatomegaly
If receiving myelofibrosis therapy, must be on a stable dose of the same regimen for at least 2 weeks prior to screen date and through the screening period
If not receiving myelofibrosis therapy, must remain off therapy for at least 2 weeks prior to screen date and through the screening period

Acceptable laboratory assessments obtained within 14 days prior to Randomization

Absolute neutrophil count (ANC) > 0.75 x 10^9/L in the absence of growth factor in the prior 7 days
Peripheral blood blast count < 10%
Aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 3 x the upper limit of the normal range (ULN) (≤ 5 x ULN if liver is involved by extramedullary hematopoiesis as judged by the investigator or if related to iron chelator therapy that was started within the prior 60 days)
Calculated creatinine clearance of ≥ 45 mL/min
Direct bilirubin ≤ 2.0 x ULN
Life expectancy > 24 weeks
Negative serum pregnancy test for female subjects (unless surgically sterile or greater than two years post-menopausal)
Males and females of childbearing potential must agree to use protocol-specified method(s) of contraception
Females who are nursing must agree to discontinue nursing before the first dose of MMB
Able to understand and willing to sign informed consent form (ICF)

Key Exclusion Criteria:

Prior splenectomy
Splenic irradiation within 3 months prior to Randomization
Use of investigational agent within 28 days prior to Randomization
Prior treatment with MMB
Hematopoietic growth factor (granulocyte growth factor, erythropoiesis stimulating agent, thrombopoietin mimetic) within 28 days prior to Randomization
Uncontrolled inter-current illness, per protocol
Known positive status for human immunodeficiency virus (HIV)
Chronic active or acute viral hepatitis A, B, or C infection, or hepatitis B or C carrier
Presence of peripheral neuropathy ≥ CTCAE Grade 2
Unwilling or unable to undergo a MRI or CT Scan per study protocol requirements

Note: Other protocol defined Inclusion/Exclusion criteria may apply.