Improved specificity of MRD monitoring in MM of second- vs first-generation MFC. (A) PCA model for the phenotypic-based discrimination between normal (n = 17) BM PCs from healthy individuals and BM clonal PCs (n = 71) from MM patients. In the two-dimensional PCA plots, every healthy individual and patient is represented by a single dot and normal or MM reference PC groups by 1 (dashed lines) and 2 (solid lines) SD curves. Phenotypic makers are ordered according to their higher vs lower significance to discriminate between normal and clonal PCs. (B-C) Phenotypically selected clonal PCs from 50 MRD-positive MM patients (blue dots) were plotted against the PCA model based on all 8 phenotypic markers available with second-generation MFC (CD38, CD138, CD19, CD27, CD45, CD56, CD81, and CD117) vs the PCA model based on 4 phenotypic markers only, available with first-generation MFC (CD38, CD19 CD45 and CD56). (D-E) TTP (D) and OS (E) according to MRD status by second-generation MFC (n = 162). A total of 54 patients had undetectable MRD or MRD levels <0.001% (MRD−ve; <10−5), 20 cases had detectable MRD in between 0.001% and 0.02% (MRD+ve; ≥10−5 to <10−4), and the remaining 88 patients had detectable MRD at 0.01% or higher levels (MRD+ve; ≥10−4).
