Inclusion Criteria:

   - Subjects must be diagnosed with primary myelofibrosis (PMF), post-polycythemia
   vera-myelofibrosis (PPV-MF) or post-essential thrombocythemia-myelofibrosis (PET-MF)
   according to the 2008 World Health Organization criteria

   - Subjects with myelofibrosis requiring therapy must be classified as high risk OR
   intermediate risk level 2 according to the prognostic factors defined by the
   International Working Group

   - Subjects with an Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1,
   2 or 3

   - Subjects who have not previously received treatment with a Janus kinase (JAK)
   inhibitor

Exclusion Criteria:

   - Subjects with a life expectancy of less than 6 months

   - Subjects with inadequate bone marrow reserve as demonstrated by specific clinical
   laboratory counts

   - Subjects with inadequate liver or renal function

   - Subjects with clinically significant bacterial, fungal, parasitic or viral infection
   which require therapy

   - Subjects with an active malignancy over the previous 5 years except specific skin
   cancers.

   - Subjects with severe cardiac conditions

   - Subjects who have had splenic irradiation within 12 months