Acute transformation of chronic lymphocytic leukemia.

A patient with chronic lymphocytic leukemia had typical cell morphology and a characteristic clinical course for 7 years. He then developed progressive disease with a rapidly rising WBC which proved resistant to chemotherapy. The cells resembled lymphoblasts. Immunoperoxidase studies demonstrated identical immunoglobulin light and heavy chains on the surface of both mature lymphocytes and lymphoblasts. Using a recently described monoclonal antibody, B5, a "blast" antigen was demonstrated on the lymphoblast cell surface, but not on the mature lymphocytes. On the basis of morphological and immunological studies, we suggest that the patient's malignant clone transformed from chronic lymphocytic leukemia to acute lymphoblastic leukemia.