Leukaemia of platelet precursors: diverse features in four cases.

Four patients are described with malignant cells of definite or probable megakaryocytic lineage in the bone marrow and blood. Megakaryocytic features were defined by morphological and cytochemical studies using light and electron microscopy, and in two cases by reaction with a monoclonal anti-platelet antibody, AN51. All patients had increased bone-marrow reticulin, which developed in less than 15 months in two cases. One of these fitted the clinical pattern of acute myelosclerosis of Lewis and Szur (now widely referred to as acute megakaryoblastic leukaemia). Three cases had unique clinical features which are described in detail. There may be several variants of megakaryocytic leukaemia, including chronic forms. One variant is associated with Down's syndrome (trisomy 21).