OBJECTIVETo analyze clinical and molecular characteristics of low-risk essential thrombocythemia (ET) in a large cohort of Chinese patients and to explore risk factors for major thrombosis and treatment strategies.

METHODSMedical records of patients with an initial diagnosis of ET from March 1982 to May 2012 in our hospital were retrospectively analyzed.

RESULTSA total of 604 low-risk ET patients were enrolled with a median follow-up of 49 months (range:0-338). 43(7.1%) patients experienced major thrombotic events. Cox proportional hazards regression revealed JAK2 V617F mutation (HR=2.279; P=0.035) and cardiovascular risk factors (CVF) (HR=2.541; P=0.006) to be risk factors for total thrombotic events, while only CVF (HR=2.633; P=0.008) was risk factor for arterial thrombosis. None of the evaluated factors was related to venous thrombosis. Patients with both JAK2 V617F mutation and CVF had a worse thrombosis- free survival than those with only one risk factor (P<0.05). In patients with JAK2 V617F or CVF alone, antiplatelet treatment (P=0.016) significantly decreased the risk of thrombosis, while those with both JAK2 V617F and CVF could benefit from cytoreductive agents (P=0.018).

CONCLUSIONChinese low-risk ET patients have a lower risk of thrombosis than Caucasian low-risk ET patients. JAK2 V617F mutation and CVF are the most significant risk factors for thrombosis. Existence of both risk factors further increases the thrombotic risk. Treatment strategies on low-risk ET patients should be made based on presence or absence of risk factors.