To identify prognostic factors affecting thrombosis-free survival (TFS) and overall survival (OS), we report the experience of a Regional cooperative group in a real-life cohort of 1,144 patients with essential thrombocythemia (ET) diagnosed from January 1979 to December 2010. There were 107 thrombotic events (9.4%) during follow-up [60 (5.3%) arterial and 47 (4.1%) venous thromboses]. At univariate analysis, risk factors for a shorter TFS were: age >60 years (P < 0.0054, 95% CI 1.18-2.6), previous thrombosis (P < 0.0001, 95% CI 1.58-4.52) and the presence of at least one cardiovascular risk factor (P = 0.036, 95% CI 1.15-3.13). Patients with a previous thrombosis occurred ≥24 months before ET diagnosis had a shorter TFS compared to patients with a previous thrombosis occurred <24 months (P = 0.0029, 95% CI 1.5-6.1); furthermore, patients with previous thrombosis occurred <24 months did not show a shorter TFS compared with patients without previous thrombosis (P = 0.303, 95% CI 0.64-3.21). At multivariate analysis for TFS, only the occurrence of a previous thrombosis maintained its prognostic impact (P = 0.0004, 95% CI 1.48-3.79, RR 2.36). The 10-year OS was 89.9% (95% CI 87.3-92.5): at multivariate analysis for OS, age >60 years (P < 0.0001), anemia (P < 0.0001), male gender (P = 0.0019), previous thromboses (P = 0.0344), and white blood cell >15 × 10(9) /l (P = 0.0370) were independent risk factors. Previous thrombotic events in ET patients are crucial for TFS but their importance seems related not to the occurrence per se but mainly to the interval between the event and the diagnosis.
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