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.