Thrombosis in patients with post-polycythemia vera myelofibrosis: incidence and risk factors

Introduction: Post-polycythemia vera (PV) myelofibrosis (Post-PV MF) is an advanced phase of natural progression of PV. Thrombosis is a major cause of morbidity and mortality in PV; however, the characteristics of thrombosis in post-PV MF have not been characterised.

Methods: The clinical and laboratory characteristics of 163 patients with post-PV MF were analysed. Kaplan-Meier and multivariate Cox analyses were used to estimate risk factors for thrombosis.

Results: During follow-up, 84 (51.5%) patients developed thrombosis, 11 (6.7%) progressed to acute leukemia, 35 (21.5%) died (20% due to thrombosis). Thrombosis-free survival (TFS) in post-PV MF was lower than that of sex- and age-matched patients with PV (P < 0.0001). The incidence of venous thrombosis was significantly higher after diagnosis of post-PV MF than before or at diagnosis; Those with V617F% ≥ 75% or absolute monocyte count (AMC) ≥1.5 × 10⁹/L demonstrated a higher risk for venous thrombosis (P < 0.05). According to multivariate Cox regression, palpable splenomegaly (hazard ratio [HR] 3.284 [95% confidence interval (CI) 1.373-7.855]; P = 0.008), age ≥ 60 years (HR 1.604 [95%CI 1.004-2.56]; P = 0.048), history of thrombosis (HR 2.767 [95%CI 1.735-4.412]; P < 0.001) were risk factors for thrombosis. In multivariable models, median TFS in post-PV MF in extremely high -, high -, intermediate -, low-risk groups were 2, 4, 9 and 13 years, respectively.

Conclusion: Patients with post-PV MF demonstrated a higher incidence of thrombosis. Palpable splenomegaly, age ≥ 60 years, history of thrombosis were independent risk factors for thrombosis.