Multiple myeloma terminating in lymphocytic leukemia with B‐lymphocyte membrane markers

The development of lymphocytic leukemia with a rapidly fatal clinical course is reported in a patient with kappa light-chain multiple myeloma treated with alkeran. The leukemic cells lacked the ultrastructural features of plasma cells but bore readily detectable B-cell markers and resembled lymphocytes under the light, transmission, and scanning electron microscopes. The leukemic phase is perhaps best defined as lymphocytic and probably represents a variant of plasma cell leukemia, in which the cells showed a degree of dedifferentiation from plasma cells to B lymphocytes. The possible relation between these 2 proliferative processes is discussed and the nature of leukemias developing in cases of plasma cell myeloma is briefly reviewed.