Lymphoblastic conversion in chronic myelogenous leukemia.

A child presented with "acute leukemia" in which the blast cells resembled lymphoblasts and had negative cytochemical staining (PAS, Sudan black, and myeloperoxidase). Remission was induced and typical adult-type chronic myelogenous leukemia (CML) followed. Cytogenetic studies initially and during remission and subsequent "acute leukemia" relapses revealed the presence of the Philadelphia chromosome abnormality. Terminal transferase assay performed on peripheral blood blast cells was markedly elevated and soft agar culture growth parameters were typical of acute lymphoblastic leukemia T and B cell marker studies revealed no markers. This case report with supportive laboratory studies suggests that a cell line with lymphoid characteristics may predominate during acute leukemic transformation. This type of subclassification of leukemia may be of importance in therapeutic planning.