MONDO_0005029 (essential thrombocythemia) is a chronic myeloproliferative neoplasm that involves primarily the megakaryocytic lineage. It is characterized by sustained thrombocytosis in the blood, increased numbers of large, mature megakaryocytes in the bone marrow, and episodes of thrombosis and/or hemorrhage. (WHO, 2008). Also known as: essential thrombocytemia, essential thrombocythaemia, essential thrombocytosis, hemorrhagic thrombocythemia, primary thrombocythemia, primary thrombocytosis.