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.