Pegylated Interferon Alfa-2a Salvage Therapy in High Risk Polycythemia Vera (PV) or Essential Thrombocythemia (ET)

The aim of this research is to look 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. It is important for patients with ET or PV who are at risk of blood clots to receive drugs which will minimize the risks of developing these blood clots but at the moment the investigators are not sure which drugs will best control the disorder. The purpose of this study is to look at the effectiveness of giving patients who have been diagnosed with ET and PV a study drug regimen using Aspirin and PEGASYS (also known as Pegylated interferon alfa-2a, instead of the standard treatment drug called Hydroxyurea (or hydroxycarbamide or Hydroxyurea), for whom this drug may not be suitable. The drug may not be suitable either because it is not adequately controlling the number of blood cells or some specific side effects occur.