Frequency and risk factors for thrombosis in idiopathic myelofibrosis: analysis in a series of 155 patients from a single institution.

Thrombosis is a frequent complication of polycythemia vera and essential thrombocythemia, but its incidence and predisposing factors in idiopathic myelofibrosis (IM) are unknown. In 18 (11.6%) of 155 patients diagnosed with IM in a single institution, 31 thrombotic events (19 arterial, 12 venous) were registered after a mean follow-up of 4.2 (s.d.: 4.5) years. In six patients, the thrombosis was simultaneous to or appeared a few months before IM diagnosis and 14 had one or more thrombotic episodes. When compared with the general population, a significant increase was observed in the incidence of venous thrombosis (odds ratio 17.5, 95% confidence interval: 10.3-31.4). At multivariate analysis, the initial variables associated with an increased risk of thrombosis were thrombocytosis (platelets >450 x 10(9)/l, P=0.001), presence of one cardiovascular risk factor (arterial hypertension, smoking, hypercholesterolemia, or diabetes, P=0.003), cellular phase of myelofibrosis (P=0.005), and Hb >11 g/dl (P=0.02). Considering post-diagnosis events, the 5-year thrombosis-free survival probability was 90.4% in the series, 80.6% for patients with platelets >450 x 10(9)/l, 82.6% for patients with one cardiovascular risk factor, and 85.1% for those in cellular phase. These results indicate an increased thrombotic risk for IM patients with hyperproliferative features and/or coexistent cardiovascular risk factors.