Inclusion Criteria:

          -  Diagnosis of primary myelofibrosis, post-polycythemia vera myelofibrosis, or
             post-essential thrombocythemia myelofibrosis

          -  Palpable spleen of > 10 cm below the left subcostal margin on physical examination at
             the screening visit OR

          -  Palpable splenomegaly of 5 to 10 cm below left subcostal margin on physical exam AND
             active symptoms of MF at the screening visit as demonstrated by presence of 1 symptom
             score ≥ 5 or 2 symptom scores ≥ 3 using the Screening Symptom Form

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

        Exclusion Criteria:

          -  Use of experimental drug therapy for myelofibrosis, or any other standard drug (eg,
             danazol, hydroxyurea, etc) with the exception of ruxolitinib within 6 months of
             starting study (combination) therapy and/or lack of recovery from all toxicities from
             previous therapy (except ruxolitinib) to Grade 1 or better

          -  Inability to swallow food or any condition of the upper gastrointestinal tract that
             precludes administration of oral medications

          -  Unwillingness to be transfused with blood components

          -  Recent history of inadequate bone marrow reserve as demonstrated by the following:

               -  Platelet count < 50 × 10^9/L in the 4 weeks before screening or platelet
                  transfusion(s) within 8 weeks before screening

               -  Absolute neutrophil count levels < 0.5 × 10^9/L in the 4 weeks before screening

               -  Subjects with peripheral blood blast count of > 10% at the screening or baseline
                  hematology assessments

               -  Subjects who are not willing to receive red blood cell (RBC) transfusions to
                  treat low hemoglobin levels

          -  Inadequate liver function at screening as demonstrated by the following:

               -  Direct bilirubin ≥ 2.0 × the upper limit of laboratory normal (ULN). (NOTE:
                  direct bilirubin will only be determined if total bilirubin is ≥ 2.0 × ULN)

               -  alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2.5 × ULN

          -  Inadequate renal function at screening as demonstrated by creatinine clearance < 50
             mL/min or glomerular filtration rate < 50 mL/min/1.73 m^2