title: Essential thrombocythemia: scientific advances and current practice.
abstract: OBJECTIVE
  Median survival in essential thrombocythemia exceeds 20 years and clinical course is usually indolent with a minority of patients experiencing thrombohemorrhagic complications. Leukemic, polycythemic, or fibrotic disease transformation in essential thrombocythemia is an infrequent occurrence with a 15-year cumulative risk of approximately 5% or less in each instance. The major incentives for this review have been the recent description of an activating JAK2 tyrosine kinase mutation (JAK2 (V617F)) in essential thrombocythemia, related myeloproliferative disorders, and the impact on clinical practice from the publication of a major treatment trial.
  
  
  RESULTS
  Several studies have reported on the occurrence of JAK2(V617F) in approximately 50% of patients with essential thrombocythemia and its presence has been associated with advanced age at diagnosis, higher hemoglobin and leukocyte levels, and increased rate of polycythemic transformation. In contrast, the mutation did not appear to affect the incidence of thrombotic, leukemic, or fibrotic events. There is increasing evidence regarding the thrombogenic role of neutrophils in essential thrombocythemia and this might partly explain the superior overall performance by hydroxyurea, compared with anagrelide, in a recent randomized study.
  
  
  CONCLUSIONS
  Although it is in vogue to consider essential thrombocythemia as more than one disease in terms of both molecular phenotype (presence or absence of JAK2(V617F)) and putative pattern of myelopoiesis (monoclonal versus polyclonal), it is yet to be shown that such differences influence either the natural history of the disease or current therapy. From a treatment standpoint, hydroxyurea is now confirmed to be the drug of choice for high-risk patients with essential thrombocythemia.
authors.affiliation: Division of Hematology, Department of Internal Medicine, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. tefferi.ayalew@mayo.edu
authors.forename: Ayalew
authors.initials: A
authors.lastname: Tefferi
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D001241:Aspirin / Q000627:therapeutic use; D001856:Bone Marrow Examination / Q000379:methods; D006801:Humans; D006918:Hydroxyurea / Q000627:therapeutic use; D017404:In Situ Hybridization, Fluorescence; D053614:Janus Kinase 2 / Q000235:genetics*; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use; D017354:Point Mutation / Q000235:genetics; D013920:Thrombocythemia, Essential / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics*; D013927:Thrombosis / Q000209:etiology
chemical_list: D000970:Antineoplastic Agents; D010975:Platelet Aggregation Inhibitors; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D001241:Aspirin; D006918:Hydroxyurea