Ruxolitinib (INCB018424) in Participants With Primary Myelofibrosis (PMF), Post Essential Thrombocythemia-myelofibrosis and Post Polycythemia Vera-myelofibrosis (PPV-MF)

An Open-Label Assessment of Safety and Efficacy of Ruxolitinib (INCB018424) in Subjects With Primary Myelofibrosis, Post- Essential Thrombocythemia Myelofibrosis, and Post-Polycythemia Vera Myelofibrosis Who Have Platelet Counts of 50 × 10^9/L to 100 × 10^9/L

To evaluate the effects of treatment with ruxolitinib (INCB018424) on spleen volume, symptoms and potential side effects in participants with PMF, PPV-MF and PET-MF who have platelet counts of 50 x 10^9/L to 100 x 10^9/L. It is anticipated that individualized dose optimization from the starting ruxolitinib level of 5 mg bid will be associated with reductions in splenomegaly, MF-associated symptoms and inflammatory cytokine levels.

Inclusion Criteria:

• Diagnosed with PMF, PPV-MF or PET-MF as confirmed by bone marrow biopsy
• Discontinuation of all drugs used to treat underlying MF disease at least 14 days prior to baseline visit
• INR <= 1.5 or PTT value < 1.5 x upper limit of normal (ULN) at study entry
• Hemoglobin level at least 6.5 g/dL at Screening visit
• Willingness to be transfused to treat low hemoglobin levels

Exclusion Criteria:

• Females who are pregnant, unable to comply with birth control use to avoid becoming pregnant or breastfeeding
• Males who cannot comply with birth control use to avoid fathering a child
• Platelet count < 50 x10^9/L or absolute neutrophil count (ANC) < 1 x10^9/L at the Screening visit
• Inadequate liver or renal function; Intracranial bleeds or invasive malignancy over the previous 2 years - international normalized ratio (INR) laboratory values cannot be > 1.5 x upper limit of normal at study entry.