Acute nonlymphocytic leukemia: heterogeneity of stem cell origin.

Four patients with acute nonlymphocytic leukemia who were heterozygous for the X-chromosome-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) were studied to determine the numbers and types of progenitor cells in which the disease arose. Both forms of enzyme were found in normal tissues, but the malignant blast cells showed only one G6PD, indicating that the disease was clonal at the time of testing. The observations that normal erythroid cells were present in two young patients at diagnosis and relapse indicate that the clone suppressed expression of normal granulopoiesis but did not prevent normal erythroid differentiation. In contrast to this situation, in two elderly patients, the disease involved stem cells multipotent for granulocytes, red cells, and platelets. These results indicate that acute nonlymphocytic leukemia is heterogeneous. In some patients, the disease is expressed in cells with differentiation restricted to the granulocyte-monocyte pathway; in others, it involves stem cells capable of differentiating to granulocytes-monocytes, platelets, and erythrocytes. This heterogeneity may reflect differences in causation and could have prognostic and therapeutic importance.