Multiple myeloma and chronic lymphocytic leukemia: parallels and contrasts.

Multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) are closely related B-cell cancers. Parallel and divergent features of these diseases are reviewed. In MM, expression of multiple hemopoietic lineage-associated antigens on the malignant cells and the substantial likelihood of progression to acute myelogenous leukemia suggest transformation of a pluripotent stem cell. In CLL, transformation more likely involves a committed B-cell progenitor. Another difference is that clonal evolution with associated cytogenetic progression is common in MM but not CLL. Other data, including studies of proto-oncogenes and tumor suppressor genes, suggest that MM results both from increased proliferation and accumulation of tumor cells, whereas tumor cell accumulation is the predominant feature of CLL. These differences may be reflected in the seemingly greater role of cytokine abnormalities in MM progression. For example, osteoclast-activating properties of some cytokines account for bone involvement in MM but not in CLL. MM and CLL share common features such as stage-dependent anemia and immune deficiency. Both diseases respond to alkylating agents but vary markedly in their sensitivity to fludarabine (CLL greater than MM) and glucocorticoids (MM greater than CLL). Differences between these diseases in progression-free interval and survival may reflect different definitions of premalignant and malignant phases rather than biologic differences. Detailed comparisons between MM and CLL may provide additional insights into these and related B-cell cancers.