QUANTITATION OF CIRCULATING PERIPHERAL-BLOOD PLASMA-CELLS AND THEIR RELATIONSHIP TO DISEASE-ACTIVITY IN PATIENTS WITH MULTIPLE-MYELOMA

Background. The analysis of peripheral blood mononuclear cells for pla sma cells and B-cell surface light chain ratios may provide additional insight on the pathogenesis of multiple myeloma and predict disease a ctivity. The goals of this study were to correlate these parameters wi th clinically determined disease activity and establish a cutoff value of circulating plasma cells that could be used in future clinical tri als. Methods. Peripheral blood samples from 84 patients with monoclona l gammopathies were analyzed by an immunofluorescence, slide-based, la beling index (LI) technique for detection of plasma cells, the LI, and light chain ratios. These parameters were compared with disease activ ity. Results. Of the 84 patients studied, 27% had inactive and 73% had active disease. The mean number of plasma cells for patients with ina ctive disease was 0.61 X 10(6)/l, compared with 139.6 X 10(6)/l for pa tients with active disease (P < 0.001). The mean ratios of involved to uninvolved light chain percentages for patients with inactive and act ive disease were 1.6 and 9.2, respectively (P = 0.002). The absolute n umber of plasma cells better predicted disease activity than the light chain ratio. By use of a cutoff value of 3 X 10(6)/l, 67% of patients with active disease were determined to have 3 X 10(6)/l or more plasm a cells, and 96% of those with inactive disease had less than 3 X 10(6 )/l plasma cells. Conclusions. These results suggest that detection of circulating plasma cells is a marker of disease activity in patients with plasma cell disorders and that an appropriate cutoff value is 3 X 10(6)/l or more circulating plasma cells.