Essential Thrombocythemia

Essential thrombocythemia (ET) is currently classified as a myeloproliferative disorder (MPD), which is a heterogeneous category of clonal stem cell diseases that also includes polycythemia vera (PV), myelofibrosis with myeloid metaplasia (MMM), chronic myeloid leukemia (CML), and atypical MPDs (1). A major advance in our understanding of the pathogenesis of MPDs was made with the recent identification of the V617F JAK2 mutation in a substantial proportion of patients, especially with PV (2–7). This discovery has had a major impact on disease classification, diagnostic approach, and in addressing research strategies in these disorders.

Among the classic MPDs (1), ET shows a longer median survival as well as lower transformation rates into acute myelogenous leukemia (AML). However, the clinical course of ET is complicated by thrombotic and hemorrhagic episodes that occur more frequently in older patients and those with previous vascular events. There is an ongoing debate as to whether the evolution to AML is part of the natural history of the disease or is related to the use of cytoreductive agents given to control the myeloproliferation and avoid vascular complications. Hence, the best strategy is to limit the use of cytotoxic therapy by stratifying patients on the basis of their risk for developing vascular events.

This chapter reviews recent progress in the management of ET with particular emphasis on four key areas: pathogenesis, diagnostic criteria, clinical course, and risk-adapted therapy.