Acute bilineage leukemia after chronic myelogenous leukemia

Blastic transformation of chronic myelogenous leukemia may involve any hematopoietic lineage, including that of lymphocytes. In a minority of cases, the blasts express characteristics of both myeloid and lymphoid cells (biphenotypic) or comprise two separate populations of myeloid and lymphoid cells (bilineage leukemia). In a coordinated effort, we used a sequence of morphologic, cytochemical, immunocytochemical, and molecular biological studies to identify a case of bilineage blastic transformation of CML with a predominance of lymphoid blasts. The patient was treated for ALL and responded. The case presented illustrates the need for greater flexibility by the physician and laboratory to determine the specific diagnostic requirements for patients with hematologic malignancy with unusual phenotypic characteristics.