Inclusion Criteria

Inclusion criteria:

- Diagnosis of Primary Myelofibrosis (MF) or Post-Polycythemia Vera MF or
Post-Essential Thrombocythemia MF, according to the 2008 World Health Organization
and International Working Group of Myelofibrosis Research and Treatment (IWG-MRT)
criteria.

- MF classified as high-risk or intermediate-risk level 2, as defined by modified
IWG-MRT criteria (IPSS) (according to Cervantes F. et. al.; at screening).

- Enlarged spleen, palpable at least 5 cm below costal margin.

- At least 18 years of age.

- Eastern Cooperative Oncology Group performance status of 0, 1, or 2 at study entry.

- The following laboratory values within 14 days prior to the initiation of IMP or
placebo:

- Absolute Neutrophil Count (ANC) ≥1.0 x 10exp9/L

- Platelet count ≥50 x 10exp9/L

- Serum creatinine ≤1.5 x Upper Limit of Normal (ULN)

- Serum amylase and lipase ≤1.5 x ULN

Exclusion criteria:

- Splenectomy.

- Any chemotherapy (eg, hydroxyurea), immunomodulatory drug therapy (eg, thalidomide,
interferon-alpha), Anagrelide, immunosuppressive therapy, corticosteroids >10 mg/day
prednisone or equivalent, or growth factor treatment (eg, erythropoietin), or
hormones (eg, androgens, danazol) within 14 days prior to initiation of IMP or
placebo; darbepoetin use within 28 days prior to initiation of IMP or placebo.
Patients who have had exposure to hydroxyurea (eg, hydrea) in the past may be
enrolled into the study as long as it has not been administered within 14 days prior
to initiation of IMP or placebo.

- Major surgery within 28 days or radiation within 6 months prior to initiation of IMP
or placebo.

- Prior treatment with a Janus Kinase 2 (JAK2) inhibitor.

- Known active (acute or chronic) Hepatitis A, B, or C; and hepatitis B and C carriers

- AST or ALT ≥2.5 x ULN

- Total Bilirubin:

- Exclude if ≥3.0 x ULN

- Patients with total bilirubin between 1.5-3.0 x ULN must be excluded if the direct
bilirubin fraction is ≥25% of the total

- Prior history of chronic liver disease (eg, chronic alcoholic liver disease,
autoimmune hepatitis, sclerosing cholangitis, primary biliary cirrhosis,
hemachromatosis, non-alcoholic steatohepatitis [NASH])

The above information is not intended to contain all considerations relevant to a
patient's potential participation in a clinical trial.