Morphologic and cytochemical characteristics of childhood lymphoblastic leukemia.

The majority of childhood acute leukemias can be classified as acute lymphoblastic leukemia and acute nonlymphocytic leukemia with light microscopy and cytochemical stains alone. However, myeloperoxidase-negative myeloblastic leukemias and megakaryoblastic leukemias, as well as some metastatic tumors, can mimic lymphoblastic leukemia when these cytologic examinations are used. Conversely, occasional cases of Sudan black B-positive ALL can be confused with myeloblastic leukemia. Thus, additional immunologic and sometimes further ultrastructural studies should complement the morphologic diagnosis of ALL. The significance of L1 and L2 subtypes of ALL is still controversial. Modern chemotherapy may have obscured any significance of this division. Future studies of lymphoblast morphology should center on biologic correlates of the L2 cytology. Little prognostic significance has been found for the morphologic variants of ALL, such as the granular and hand-mirror cell types. It is important not to confuse granular ALL with acute myeloblastic leukemia. Functional immunologic studies may help in delineating the cause of uropod formation in hand-mirror variant ALL.