Long-term Follow-up of 386 Consecutive Patients with Essential Thrombocythemia: Safety of Cytoreductive Therapy

Cytotoxic agents like Hydroxyurea, Busulfan and Interferon-alpha are to date the most commonly used therapeutic approaches in Essential Thrombocythemia (ET). However, few data on the efficacy and safety of these agents in the long-term are currently available. We report a retrospective analysis of the long-term outcome of 386 consecutive ET patients, followed at single Institution for a median follow-up of 9.5 years (range, 3-28.5). Cytoreductive therapy was administered to 338 patients (88%), obtaining a response in 86% of cases. Forty-five patients (12%) experienced a thrombosis. Among baseline characteristics, only history of vascular events prior to ET diagnosis predicted a higher incidence of thrombosis. Evolution in acute leukemia/myelofibrosis occurred in 6 (1,5%) and 20 (5%) patients, and was significantly higher in patients receiving sequential cytotoxic agents. Overall survival was 38% at 19 years and was poorer for patients older than 60 years, with higher leukocytes count (>15 x 10(9)/L), hypertension and mellitus diabetes at ET diagnosis and for patients experiencing a thrombotic event during follow-up. Cytoreductive therapy was effective in decreasing platelet number with negligible toxicity; however, thrombocytosis control did not reduce the incidence of thrombosis and, for patients who received sequential therapies, the probability of disease evolution was higher and survival was poorer.