Phase 2 Study in Japanese Patients With Intermediate-2 or High Risk Primary Myelofibrosis, Post-Polycythemia Vera Myelofibrosis, Post-Essential Thrombocythemia Myelofibrosis With Splenomegaly

Inclusion criteria : * Diagnosis of primary or post-polycythemia vera or post-essential thrombocythemia myelofibrosis * Myelofibrosis classified as high-risk or intermediate-risk level 2 * Enlarged spleen, palpable at least 5 cm below costal margin * Active symptoms of myelofibrosis * At least 20 years of age * Eastern Collaborative Oncology Group (ECOG) performance status (PS) of 0, 1, or 2 at study entry * Absence of active malignancy other than myelofibrosis * Written informed consent to participate. Exclusion criteria: * Splenectomy. * Any recent chemotherapy (eg, hydroxyurea), immunomodulatory drug therapy (eg, thalidomide, interferon-alpha), immunosuppressive therapy, corticosteroids \>10 mg/day prednisone or equivalent, or growth factor treatment (eg, erythropoietin), hormones (eg, androgens, danazol) within 14 days prior to initiation of study drug. * Major surgery therapy within 28 days or radiation including spleen radiation within 6 months prior to initiation of study drug. * Concomitant treatment with or use of pharmaceutical or herbal agents known to be moderate or severe inhibitors or inducers CYP3A4. * Active acute infection requiring antibiotics. * Uncontrolled congestive heart failure (New York Heart Association Classification 3 or 4), angina, myocardial infarction, cerebrovascular accident, coronary/peripheral artery bypass graft surgery, transient ischemic attack, or pulmonary embolism within 3 months prior to initiation of study drug. * Participation in any study of an investigational agent (drug, biologic, device) within 30 days, unless during nontreatment phase. * Prior treatment with a JAK 2 Inhibitor. * Treatment with aspirin in doses \>150 mg/day * Known human immunodeficiency virus or acquired immunodeficiency syndrome-related illness. * Pregnant or lactating female. Once the lactating female stop and participate in the study, she cannot re-start feeding the baby. * Women of childbearing potential, unless using effective contraception while on study drug. Otherwise patients must be post-menopausal (at least 1 years from last menstruation without other medical reason), or surgically sterile. * Known active (acute or chronic) Hepatitis A, B, or C; and hepatitis B and C carriers. * 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.