OBJECTIVETo investigate the clinical characteristics and long-term outcome of Chinese young patients (≤40 years) with essential thrombocythemia(ET), and to develop a thrombosis predicting model specific for young patients with ET, so as to provide a new evidence for risk stratification and treatment.

METHODSMedical records of 125 Chinese young patients with newly diagnosed of ET were retrospectively analyzed.

RESULTSThe median age at diagnosis was 32 (18-40) years old, with 37 males and 88 females. During follow-up, 18 patients (14.4%) experienced major thrombotic events. JAK2 V617F (HR=8.895, P=0.001), history of thrombosis (HR=8.001, P<0.001) and WBC≥12.0×10/L (HR=5.225, P=0.002) were independent risk factors for thrombosis. The incidence of thrombosis and risk factors in young patients were different from that in general ET population, so a thrombosis predicting model specific for young patients with ET was developed. In this model, JAK2 V617F (score 2), history of thrombosis (score 2) and WBC≥12.0×10/L (score 1) were used to divide the patients into low risk (score 0), intermediate risk (score 1-2) and high risk (score≥3) groups. These 3 groups exhibited significantly different thrombosis-free survival (χ=32.223, P<0.001). Antiplatelet treatment could prevent the occurrence of thrombosis (HR=0.081, P<0.001), while cytoreductive agents significantly decreased the risk of thrombosis only in intermediate and high risk groups (14.3% vs 36.4%, χ=4.416, P=0.036). Seven patients (5.6%) evolved to myelofibrosis, and one of them finally progressed in to acute leukemia. The only risk factor for evolution was WBC≥15.0×10/L (χ=5.434, P=0.020). Neither antiplatelet treatment nor cytoreductive agents could prevent disease progression.

CONCLUSIONThe incidence of thrombosis and risk factors in young patients with ET are different from that in general ET population. The thrombosis-predicting model specific for young patients with ET is useful for guiding therapeutic decisions.