Biology of the Transition of Monoclonal Gammopathy of Undetermined Significance (MGUS) to Multiple Myeloma

Abstract

Background

Approximately 25% of patients with monoclonal gammopathy of undetermined significance (MGUS) eventually develop multiple myeloma (MM) or a related plasma cell disorder that is universally fatal. In this report, we examine the changes that occur in the clonal plasma cell that are likely to be important in the progression of MGUS to active myeloma.

Methods

Studies that investigate the mechanisms involved in the multistep pathogenesis of monoclonal gammopathies are reviewed. Cytokines such as IL- 6 and IL-1β, adhesion molecules, viruses, and oncogenes including ras, bcl-2, Rb, and p53 are discussed.

Results

IL-1β is produced by plasma cells from virtually all MM patients but is undetectable in most MGUS patients. IL-1β has potent osteoclast activating factor activity, can increase the expression of adhesion molecules, and can induce paracrine IL-6 production. The increased production of adhesion molecules could explain why myeloma cells are found predominantly in the bone marrow. Subsequently, these “fixed” monoclonal plasma cells could now stimulate osteoclasts through the production of IL-1β and paracrine generation of IL-6 resulting in osteolytic disease. With continued progression of the myeloma, the monoclonal plasma cells may later acquire the ability to produce IL-6 in an autocrine fashion that will be manifested clinically by an elevated labeling index.

Conclusions

A better understanding of the progression of MGUS to myeloma may lead to novel therapeutic strategies to prevent the development of MM.