If you choose to join this study, you will go through a screening period to find out if you are eligible. During this screening period, you will:

• Have a physical exam
• Have an ECG
• Have blood draws
• Have a tumor biopsy

If you are eligible to join, you will proceed to the study drug period. During this period, you will get a random assignment (like a coin flip) to 1 of 2 groups:

• Group 1 will take the study drug
• Group 2 will take a comparison drug (anagrelide, busulfan, interferon alfa, or ruxolitinib)

You will take the study drug or comparison drug by mouth each day for up to one year. You will visit our clinic every other week during the first 12 weeks you take the study or comparison drug, and then visit our clinic once per month after the first 12 weeks have passed If you finish a one-year course of the study drug regimen, you will have the option to extend your participation in the study. We will let you know at this time if you were in Group 1 or Group 2. If you were in Group 1, you can continue to take the study drug. If you were in Group 2, you will have the option to switch over to the study drug or to continue to take the same drug you were assigned. This study extension will last for up to 2 years. You will visit our clinic every 4 weeks if you choose to participate in the extension. At various visits during the study, you will complete physical exams, have blood draws, have ECGs, answer questionnaires, have swabs taken from your cheek, and have bone marrow samples taken.