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WHO Classification of Tumours
Essential thrombocythaemia
Tumours of haematopoietic and lymphoid tissues


Essential thrombocythaemia (ET) is a chronic myeloproliferative neoplasm (MPN) that involves primarily the megakaryocytic lineage. It is characterized by sustained thrombocytosis ≥450x109/L in the peripheral blood (PB), increased numbers of large, mature megakaryocytes in the bone marrow (BM), and clinically by episodes of thrombosis and/or haemorrhage. Because there is no known genetic or biological marker specific for ET, other causes for thrombocytosis must be excluded, including other MPN, inflammatory and ­infectious disorders, haemorrhage and other types of haematopoietic and non-haematopoietic neoplasms. The presence of a BCR-ABL1 fusion gene excludes the diagnosis of ET. The diagnostic criteria are outlined in Table 2.06

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Introduction: Myeloid Neoplasms