Classification of acute leukemia.

The classification of acute leukemia has almost invariably been based on the morphologic diagnosis into two broad categories: acute lymphocytic and acute myeloid leukemia. Despite the wide range of morphologic variation in both groups, strict criteria to define the subgroups have only recently been proposed. The conventional markers for B and T cells are now being applied to leukemic cells as are cytochemistry and electron microscopy, terminal deoxynucleotidyl transferase, serum lysozyme, and surface markers, E-rosettes, membrane immunoglobulin, antinull acute lymphocytic leukemia antiserum, and Fc and C3 receptors. The myelodysplastic syndromes may mimic acute leukemia and it is important that they be identified and treated appropriately. The high incidence with which chronic myelomonocytic leukemia terminates in acute leukemia suggests that it is a preleukemic condition, whereas refractory anemia with excess blasts and acquired idiopathic sideroblastic anemia may have long, drawn-out courses. Only a small population of patients with the latter conditions develop acute leukemia.