Thrombosis is a major cause of morbidity and mortality in polycythemia vera (PV). Post PV myelofibrosis (MF) is the advanced phase in the natural progression of PV. To explore the risk factors for thrombosis in post-PV MF, clinical characteristics, laboratory characteristics, the incidence of thrombosis and survival were retrospectively analyzed in a cohort of 163 Chinese patients with post-PV MF. The Kaplan-Meier method and multivariate Cox analysis were used to identify the risk factors and a risk model for thrombosis was established. Among the 163 patients, the median follow-up duration was 6 (1-18) years. During follow-up, 84 (51.5%) patients developed thrombosis, 11 (6.7%) patients progressed to acute leukemia, and 35 (21.5%) patients died (20% of whom died due to thrombosis). The 5-year, 10-year, and 15-year thrombosis-free survival (TFS) rates were 59.8%, 28.2%, and 9%, respectively. The TFS time of the post-PV MF patients was significantly lower than that of the age- and sex-matched PV patients (P<0.001). The incidence of venous thrombosis was significantly higher after the diagnosis of post-PV MF than before or at the time of the diagnosis, and the proportions of patients with JAK 2 V617F allele burden ≥75% or absolute monocyte count ≥1.5×10 9/L was significantly higher in the venous thrombosis group than in the group without venous thrombosis (P<0.05). Multivariate analysis showed that palpable splenomegaly (P=0.008, HR=3.284, 95% CI [1.373,7.855]), age ≥60 years (P=0.048, HR=1.604, 95% CI [1.004,2.56]), and a history of thrombosis (P<0.001, HR=2.767, 95% CI [1.735, 4.412]) were risk factors for thrombosis in post-PV MF patients, then a risk model for thrombosis was established according to these data. The median TFS durations in patients in the extremely high-risk group, high-risk group, intermediate-risk group, and low-risk group were 2 years, 4 years, 9 years, and 13 years, respectively. In summary, post-PV MF patients have a higher incidence of thrombosis. Reducing the volume of the spleen and the allele burden of JAK2 V617F is critical to prevent thrombosis in post-PV MF patients.


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