FIGURE 1.

A, Minimal residual disease (MRD) data (¹⁰log-transformed percentage of MRD cells) obtained using the EuroFlow approach, including CD38-multiepitope (ME) vs MRD data obtained using VS38c. The correlation coefficient for all samples together was 0.998 (P < .001); similar numbers were obtained if the 2 groups (with and without daratumumab) were analyzed separately. The samples obtained from patients treated without (n = 14) or with daratumumab (n = 15) are shown in closed and open circles, respectively. Fifteen samples (8 from patients not treated with daratumumab and 7 from patients treated with daratumumab) were MRD negative by both approaches and are shown in the bottom left this plot. B, Mean fluorescence intensities (MFIs) of CD38-ME and VS38c on B cells (B), normal plasma cells (PC), and multiple myeloma (MM) cells (if present at levels equal to or above 0.01%) in patients without (n = 14) or with daratumumab treatment (+ dara; n = 15). For VS38c, no significant differences were observed for the MFI values of PC and MM cells, independent of daratumumab treatment. For CD38, expression was highest on normal PC from patients not treated with daratumumab; MM cells from such patients showed a tendency for lower CD38 expression levels (P = .06). In patients treated with daratumumab, CD38 expression on B cells and normal cells was significantly lower compared with these cells in patients not treated with daratumumab (P < .05), and the same tendency was present for MM cells (P = .09). All P values were based on 2-tailed Mann-Whitney tests. The red lines represent the median MFI value of the group. The black lines on top of the figure indicate statistically significant differences between the 2 groups.