Additional Study Information: The purpose of this study is to collect information on whether idasanutlin is effective in treating polycythemia vera (a slow-growing blood cancer in which your bone marrow makes too many red blood cells) and what effects, good or bad, idasanutlin has on you. Idasanutlin is an experimental drug, which means Health Authorities (such as the US FDA) have not approved it for the treatment of PV or any other form of cancer. If you are eligible, you may participate in this study for approximately 2 years.