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.