This research is looking at two conditions, Essential Thrombocythemia (ET) and Polycythemia Vera (PV). ET causes people to produce too many blood cells called platelets and PV causes too many platelets and red blood cells to be made. Platelets are particles which circulate in the blood stream and normally prevent bleeding and bruising. Having too many platelets in the blood increases the risk of developing blood clots, which can result in life threatening events like heart attacks and strokes. When the number of red blood cells is increased in PV this will slow the speed of blood flow in the body and increases the risk of developing blood clots.
The purpose of this study is to look at the effectiveness of giving participants who have been diagnosed with ET or PV one of two different study regimens over time. The study subject will be followed for their condition for about 5 years. The subject will be randomized into one of two study regimens, either Pegylated Interferon Alfa-2a (PEGASYS) or Aspirin and Hydroxyurea (also called Hydroxycarbamide). The subject must be newly diagnosed or already receiving treatment for either PV or ET. Each of the study drugs used in this study is already being used to treat subjects with ET or PV currently, but the investigators are unsure which study drug is better.