A Study of INCB050465 in Combination With Ruxolitinib in Subjects With Myelofibrosis

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