Clinical study - Hématologie Leucémie

The hypothesis is that efficient prevention of thrombosis with aspirin at diagnosis becomes less useful once patients have achieved a hematologic response (HR) and/or that this benefit is hampered by an increased hemorrhagic risk especially in elderly patients.;Hence, investigator propose a prospective randomized study to assess the benefit / risk ratio of aspirin maintenance in high risk Essential thrombocythemia (ET) patients, in hematological response on Hydroxyurea.