Main Inclusion Criteria: All subjects must meet ALL of the following inclusion criteria to
be enrolled. There are additional inclusion criteria.

   - Male and female subjects aged 18 (or the country specific minimum age of consent >18)
   years or older.

   - Meet revised 2016 World Health Organization (WHO) criteria for the diagnosis of
   polycythemia vera.

   - At least 3 phlebotomies due to inadequate hematocrit control in 6 months before
   randomization or at least 5 phlebotomies due to inadequate hematocrit control in 1
   year before randomization.

   - CBC values immediately prior to randomization:

      1. Hematocrit <45%,

      2. WBC 4000/μL to 20,000/μL (inclusive), and

      3. Platelets 100,000/μL to 1,000,000/μL (inclusive)

   - Subjects receiving cytoreductive therapy at randomization must be on a stable PV
   therapy regimen.

   - Subjects treated with phlebotomy alone at randomization must have stopped
   cytoreductive therapy 2 to 6 months before screening.

Main Exclusion Criteria: Subjects must meet NONE of the following exclusion criteria to be
enrolled. There are additional exclusion criteria.

   - Clinically meaningful laboratory abnormalities at Screening.

   - Subjects who require phlebotomy at hematocrit levels lower than 45%.

   - Clinically significant thrombosis (e.g., deep vein thrombosis or splenic vein
   thrombosis) within 2 months prior to randomization.

   - Active or chronic bleeding within 2 months prior to randomization.

   - History of invasive malignancies within the last 5 years, except localized cured
   prostate cancer and cervical cancer.

   - Subjects with in situ or stage 1 squamous cell carcinoma of the skin, in situ or stage
   1 basal cell carcinoma of the skin, or in situ melanoma of the skin identified during
   screen unless the cancer is adequately treated before randomization.

   - Received Busulfan, Pipobroman or 32Phosphorus within 7 months prior to screening.