, Volume 4, Issue 5, pp 381-388
Date: 28 Jul 2009

Essential thrombocythemia: past and present

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Abstract

Essential thrombocythemia (ET) is a clonal myeloproliferative disorder characterized by sustained increase in platelet number and tendency for thromboembolism. A somatic point mutation that causes a constitutive activation of the JAK2 gene is found in one in two ET patients. ET is more common in women, its incidence being 0.6–2.5/100,000 patient/year and the median age at diagnosis is 65–70 years. ET can affect all age groups, including children (0.09 cases/year), and is often diagnosed in the third–fourth decade of life. Rare cases of familial ET have been reported. Miscarriages are 3–4 times more common among women with ET than in the general population, especially in patients carrying JAK2V617F. Microvascular disturbances are typical of ET, but a major thrombosis (2/3 arterial and 1/3 venous; 1, 2–3% patient/year) is the main cause of morbidity and mortality. Age over 60 years and/or previous thrombosis are validated risk factor for thrombosis. Hemorrhages occur in 0.33% patient/year, mainly in those with a platelet count over 1,500 × 109/L. Progression to myelofibrosis and leukemia is more common in patients carrying the JAK2V617F mutation, and is estimated to occur in 0.16% and 0.12% patient/year, respectively. The ET-related mortality ratio with respect to the general population is 1:1, while for polycythemia vera it is 1.6:1. Low-dose aspirin is useful for microvascular disturbances, and in the primary and secondary prevention of major thrombosis in high-risk patients, but it is not recommended in patients with a platelet count over 1,500 × 109/L. Hydroxyurea is used as first-line treatment in high-risk patients. Other drugs available are alpha-interferon, anagrelide, pipobroman and busulphan.