Detection of peripheral blood plasma cells as a predictor of disease course in patients with smouldering multiple myeloma.

We evaluated the number and labelling index of circulating peripheral blood monoclonal plasma cells (PBPC) in 57 patients with newly diagnosed smouldering multiple myeloma (SMM) to determine if these measurements could distinguish SMM from active multiple myeloma (MM). The PBPC were detected by a sensitive slide-based immunofluorescence procedure that identified PC by their morphology and monoclonal light chain staining. The presence of abnormal PBPC (defined as an increase in number or proliferative rate of circulating monoclonal plasma cells) was correlated with patient status at 6 and 12 months after testing. 16 of the 57 patients progressed within 12 months and 63% of these had abnormal PBPC. In contrast, only 10% (4/41) of those patients who remained stable had abnormal PBPC. The median time to progression for patients with abnormal PBPC was 0.75 years, compared to 2.5 years for those patients without abnormal PBPC (P < 0.01). The detection of PBPC is important and helps to identify patients with active MM when other parameters suggest SMM. The lack of abnormal PBPC suggests SMM, and these patients may have a stable course without the need for immediate chemotherapy.