Heterogeneous acute leukemias.

We have reported two cases of Philadelphia-chromosome-negative acute leukemia with heterogeneous populations of leukemic cells and reviewed six cases from the literature. The cases were identified by several methods, including morphology, cytochemistry, enzymatic analysis, cytogenetic analysis, and electron microscopy. Predisposing factors were probably present in three cases and may partially account for the seemingly increasing incidence, as has been the experience with other secondary leukemias. The prognosis was variable, but most of the complete remissions were seen only when lymphocytic and nonlymphocytic antileukemic chemotherapeutic regimes were used. The occurrence of these unusual acute leukemias strongly supports the concept of a lymphoid-myeloid stem cell.