Coexistence of myeloid and lymphoid neoplastic subpopulations in chronic myelogenous leukemia.

Serial cytogenetic studies have been performed on a child with Philadelphia chromosome (Ph1)-positive chronic myelogenous leukemia (CML) and correlated with clinical, morphologic, and cytochemical data in an attempt to elucidate further the natural history of leukemia progression observed in this disease. Once the initial blast crisis had occurred, two genetically different leukemic clones of cells, one presumably having arisen from the other, coexisted throughout the remainder of the patient's course. The initial clone comprised differentiating myeloid cells, while the second clone appeared on morphologic and cytochemical grounds to be lymphoid and blastic. A dynamic equilibrium existed between these two populations of cells, with the balance altered by chemotherapy and/or other selective pressures. The leukemic progression demonstrated in this case is consistent with the concept of clonal evolution of malignant cell populations. In planning therapy, it may be necessary to consider each of these coexistent clones and their different therapeutic requirements.