OBJECTIVE: To describe the long-term natural history of essential thrombocythemia (ET) in terms of life expectancy, risk of disease transformation into a more aggressive myeloid disorder, and prognostic factors for both survival and disease complications. PATIENTS AND METHODS: The study population consisted of a consecutive cohort of patients seen at the Mayo Clinic in Rochester, Minn, in whom a diagnosis of ET was established before 1992, thus allowing a minimum of 10 years of potential follow-up. The conventional criteria-based diagnosis was confirmed by bone marrow biopsy in all instances. RESULTS: A total of 322 patients were studied (median age, 54 years; median follow-up, 13.6 years). With a median survival time of 18.9 years, survival in the first, decade of disease was similar to that of the control population (risk ratio, 0.72; 95% confidence interval, 0.50-0.99) but became significantly worse thereafter (risk ratio, 2.21; 95% confidence interval, 1.74-2.76). Multivariable analysis identified age at diagnosis of 60 years or older, leukocytosis, tobacco use, and diabetes mellitus as independent predictors of poor survival. A 2-variable model based on an age cutoff of 60 years and leukocyte count of 15 × 109/L resulted in 3 risk groups with significant difference in survival. In addition, age at diagnosis of 60 years or older, leukocytosis, and history of thrombosis were independent predictors of major thrombotic events. The risk of leukemic or any myeloid disease transformation was low in the first 10 years (1.4% and 9.1%, respectively) but increased substantially in the second (8.1% and 28.3%, respectively) and third (24.0% and 58.5%, respectively) decades of the disease. CONCLUSION: Life expectancy in patients with ET is significantly worse than that of the control population. Leukocytosis is identified as a novel independent risk factor for both inferior survival and thrombotic events.
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