Essential Thrombocythemia (ET)

Abstract

Essential thrombocytosis is also known as essential thrombocythemia (ET). It was first recognized in 1934; however, at that time, it was described as hemorrhagic thrombocythemia. Essential thrombocytosis is one of the myeloproliferative neoplasms. It was classified as a myeloproliferative neoplasm in 1951 by Damesheck.[1] Myeloproliferative neoplasm includes polycythemia vera, primary myelofibrosis, and essential polycythemia.[2] The three types of myeloproliferative neoplasm are similar as they share the same mutations. Approximately 55% of patients with essential thrombocytosis have the JAK2 mutation.[3] Essential thrombocytosis is characterized by thrombocytosis with the presence of megakaryocytic hyperplasia in the bone marrow. Due to thrombocytosis, there are risks of vascular events such as thrombosis and hemorrhage and sometimes the conversion to a blast phase of myelofibrosis.[4] According to the World Health Organization, essential thrombocytosis is a disease that occurs when the platelet count is more than 450000 with the presence of Janus kinase 2 (JAK2), Calreticulin (CALR) or myeloproliferative leukemia virus oncogene (MPL) mutation, lacking clonal or reactive causes.[5]  This review article will focus on reviewing the etiology, epidemiology, pathophysiology, evaluation, and treatment of this disease. CN - NBK539709