Abstract
A 31-year-old man was admitted to our hospital in January, 1985, because of high fever. Hematological examination revealed hemoglobin of 6.5 g/dl, platelet count of 2.1×104/μl and leukocyte count of 3,400/μl with 55.0% blasts, 0.5% neutrophils and 44.5% lymphocytes. Twenty five percent of the blast cells were small, with scanty cytoplasm and prominent nucleolus, while the rest (30.0%) were large, having abundunt cytoplasm with azur granules and Auer body (Auer body-positive cells: 6.5%). A bone marrow aspirate was hypercellular, with 81.2% blast cells consisted of 37.2% small blast cells and 44.0% large blast cells (Auer body positive cells: 13.6%). Thirty percent of blast cells in the bone marrow were positive for myeloperoxidase. Cytogenetic analysis revealed a normal karyotype. The surface marker of mononuclear cells identified by mouse monoclonal antibodies were OKIa1+ 51.9%, MY9+ 15.9%, Leu12+ 49.3%, B4+ 17.7% in peripheral blood, and OKIa1+ 74.9%, MY9+ 35.2%, Leu12+ 43.3%, B4+ 23.4% in bone marrow. These findings indicated that blast cells of the present case were composed of the two distinct populations of myeloid and lymphoid blast cells. The electronmicroscopic findings of the blast cells also suggested the existence of two population. Acute leukemia has been cosidered to be characterized by the proliferation of committed lymphoid or myeloid stem cells, but the existence of acute mixed leukemia suggested that some cases of acute leukemia were caused by leukemic transformation occurring in the uncommitted multipotential progenitor cells of both lymphoid and myeloid cells as observed in chronic myelocytic leukemia.
