Study of Efficacy and Safety in Polycythemia Vera Subjects Who Are Resistant to or Intolerant of Hydroxyurea: JAK Inhibitor INC424 (INCB018424) Tablets Versus Best Available Care: (The RESPONSE Trial)

Inclusion Criteria:

- Participants diagnosed with PV for at least 24 weeks prior to screening according to
the 2008 World Health Organization criteria

- Participants resistant to or intolerant of hydroxyurea

- Participants with a phlebotomy requirement

- Participants with splenomegaly (palpable or non-palpable) and a spleen volume, as
measured by MRI (or CT in applicable participants ), of greater than or equal to 450
cubic centimeters

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

Exclusion Criteria:

- Women who are pregnant or nursing

- Participants with inadequate liver or renal function

- Participants with significant bacterial, fungal, parasitic, or viral infection
requiring treatment

- Participants with an active malignancy within the past 5 years, excluding specific
skin cancers

- Participants with known active hepatitis or HIV positivity

- Participants who have previously received treatment with a JAK inhibitor

- Participants being treated with any investigational agent