Observation versus antiplatelet therapy as primary prophylaxis for thrombosis in low-risk essential thrombocythemia

Abstract

The effectiveness of antiplatelet therapy as primary prophylaxis for thrombosis in low-risk essential thrombocythemia (ET) is not proven. In this study, the incidence rates of arterial and venous thrombosis were retrospectively analyzed in 300 lowrisk patients with ET treated with antiplatelet drugs as monotherapy (n = 198) or followed with careful observation (n = 102). Follow-up was 802 and 848 person-years for antiplatelet therapy and observation, respectively. Rates of thrombotic events were 21.2 and 17.7 per 1000 person-years for antiplatelet therapy and observation, respectively (P = .6). JAK2 V617F-positive patients not receiving antiplatelet medication showed an increased risk of venous thrombosis (incidence rate ratio [IRR]: 4.0; 95% CI: 1.2-12.9; P = .02). Patients with cardiovascular risk factors had increased rates of arterial thrombosis while on observation (IRR: 2.5; 95% CI: 1.02-6.1; P = .047). An increased risk of major bleeding was observed in patients with platelet count greater than 1000 × 109/L under antiplatelet therapy (IRR: 5.4; 95% CI: 1.7-17.2; P = .004). In conclusion, antiplatelet therapy reduces the incidence of venous thrombosis in patients with JAK2-positive ET and the rate of arterial thrombosis in patients with associated cardiovascular risk factors. In the remaining low-risk patients, this therapy is not effective as primary prophylaxis of thrombosis, and observation may be an adequate option. © 2010 by The American Society of Hematology.