Risk factors of long-term incidences of thrombosis, myelofibrosis and evolution into malignance in polycythemia vera: a single center experience from China.

To find out risk factors of incidences of long-term complications of thrombosis, myelofibrosis with myeloid metaplasia (MMM) and evolution into malignance in Chinese PV patients, we evaluated 320 PV patients referred to our center from April 1984 to June 2005 by Kaplan-Meier estimation and Cox proportional hazards models. A total of 250 events of thrombosis were observed in 138 (43.13%) patients. Advanced age, prior thrombosis and hemoglobin out of control were statistically significant risk factors of incidences of thrombotic events. A total of 43 patients progressed into MMM at a median time of 84 (7-240) months, higher white blood cell (WBC) count, splenomegaly, receiving alkylating agent and hydroxycarbamide were associated with the progression into MMM. During the follow-up time, 11 and 2 patients died of fatal complications of thrombosis and acute myeloid leukaemia (AML), respectively. These results suggest that advanced age, prior thrombosis and hemoglobin out of control contributed to relatively high incidence of thromboembolism; higher WBC count, splenomegaly, receiving alkylating agent and hydroxycarbamide were risk factors of evolution to MMM. The main poor factors that influenced the survival of Chinese PV patients were incidences of thromboembolism and evolution into AML.