Detailed immunophenotypic features of paired BM clonal PCs vs CTCs from 15 MM patients. (A) Notched boxes represent the 25th and 75th percentile values of the ratio between the amount of FSC, SSC, or antigen MFI expression per paired CTCs/BM clonal PCs; the line in the middle and vertical lines correspond to the median value and both the 10th and 90th percentiles, respectively. (B) The corresponding iPEPs for each patient are shown. The iPEP of BM clonal PCs is represented by 1 and 2 SD lines, whereas their paired individual CTCs are represented by black dots. Each patient-specific iPEP is represented using the automated population separator (APS1) plot based on a graphical representation of principal component 1 (x-axis) vs principal component 2 (y-axis) for a total of 25 parameters studied (23 phenotypic markers plus FSC and SSC). In 12 of 15 patients (cases 1, 3, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15) CTCs clustered in a unique area of the whole space occupied by their paired BM clonal PCs, whereas in the remaining cases (patients 2, 5, 7) CTCs were spread throughout the whole BM clonal PC compartment.