Impact of leukocytosis on thrombotic risk and survival in 532 patients with essential thrombocythemia: a retrospective study

Established risk factors for thrombosis in essential thrombocythemia (ET) include age (a parts per thousand yen60 years) and previous vascular events. Recently, also leukocytosis has been proposed in risk stratification of ET patients. We report a retrospective study on 532 ET patients followed for a median of 7.6 years. Sixty-four patients (12%) developed 95 thrombotic events during follow-up. Together with the high-risk condition, a white blood cell (WBC) value above 11 x 10(9)/L, corresponding to the fourth percentile value, significantly correlated with a higher thrombotic risk (p = 0.033) by Cox proportional hazards. Moreover, the cumulative risk of thrombosis was significantly higher in high-risk patients with WBC > 11 x 10(9)/L. JAK2 V617F mutation did not correlate with thrombosis. Overall, 123 (23%) patients died. Three independent parameters were noted as prognostic factors for survival in multivariate analysis: age > 60 years, leukocytosis > 11 x 10(9)/L, and hemoglobin level below normal values. Based on these parameters, three groups of risk were defined, with significantly different survivals. Baseline leukocytosis correlated with a higher thrombotic risk in high-risk patients and identified a cohort of patients with worse survival.