Detection of malignant cells in the peripheral blood of patients with multiple myeloma: clinical implications and research applications.

OBJECTIVE: To review the methods for detecting and quantifying malignant cells in the peripheral blood (PB) and to correlate such cells with the activity of multiple myeloma (MM).
DESIGN: Results of personal investigations and studies reported in the literature were summarized.
RESULTS: MM is characterized by a monoclonal proliferation of plasma cells in the bone marrow. Although usually clinically inapparent, these plasma cells can circulate in the PB and be detected by use of sensitive immunofluorescence, flow cytometric, or molecular genetic techniques. The detection of these cells is clinically important because they correlate with disease activity. As MM progresses, the plasma cells appear in greater numbers in the PB. When patients respond to chemotherapy, the number of circulating plasma cells decreases.
CONCLUSION: Determining the molecular, immunologic, and morphologic characteristics of the circulating cells is important for improving our understanding of the pathogenesis of MM and deciding which cells to target therapeutically.