PHENOTYPIC CHARACTERISTICS OF ACUTE MEGAKARYOCYTIC LEUKEMIA AND TRANSIENT ABNORMAL MYELOPOIESIS

By immunophenotyping and ultrastructural cytochemistry, the disorders involving megakaryocytic lineage cells have been clarified. These diso rders are termed acute megakaryocytic leukemia (AMKL) and transient ab normal myelopoiesis (TAM). The characteristics of blasts in these diso rders have been extensively investigated from various standpoints incl uding cytochemistry, cytogenetics, ultrastructure and in vitro-colony differentiation. The target cells of AMKL and TAM are immature cells c lose to stem cells which are capable of differentiating into lineage c ells such as megakaryocytes, erythrocytes and myeloid cells. Phenotypi cally, these blasts frequently express antigens appearing at an early stage in the hematopoietic differentiation pathway. They thus often em erge as mixed phenotypes as seen in mixed lineage leukemia of immature cell origin.