Long-term management of thrombocytosis in essential thrombocythaemia.

Essential thrombocythaemia (ET) is an acquired myeloproliferative disorder with a prolonged clinical course and a near-normal life expectancy. Therapy is stratified according to risk of thrombohaemorrhagic events. In high-risk patients, platelet reduction is generally recommended. In intermediate-risk patients, therapy should be considered depending on the severity of associated risk factors, especially cardiovascular. In low-risk patients, a watch-and-wait approach is appropriate. Hydroxycarbamide is generally first-line therapy. Concerns for possible leukemogenicity make anagrelide or interferon-alpha possible choices in younger patients and those who are resistant or intolerant to hydroxycarbamide. Each pharmacotherapy is associated with specific long-term risks and benefits. The potential risk of major bleeding is the main drawback of aspirin. Hydroxycarbamide is an established, effective drug for ET, but it may increase the risk of transformation to acute myeloid leukaemia and may give mucocutaneous ulcers. Anagrelide is a licensed treatment that also reduces platelet counts and is generally well tolerated, with evidence that some common side effects diminish over time. Anagrelide can have cardiac effects due to inhibition of phosphodiesterase III and therefore requires cautious use in patients with cardiac insufficiency. There is no evidence of leukaemogenicity with anagrelide or interferon-alpha therapy. Interferon-alpha is the only treatment suitable for use during pregnancy, although it is not licensed in ET. While it is effective for platelet reduction, the use of interferon-alpha is restricted by psychiatric side effects. Our knowledge of the optimum pharmacotherapy for each patient with ET continues to evolve through research and clinical trials, particularly into the molecular basis of the disease.