CXCR4 and SDF1 expression in patients with MM. (A) Surface expression of CXCR4 on plasma cells in the peripheral blood (PB) and bone marrow (BM) of patients with MM. Median percentage expression of CXCR4 in plasma cells in the PB was 60% (range, 9%-96%) compared with 26.4% (range, 1%-81%) in the BM of patients with active MM (P = .001). (B) Intracellular expression of CXCR4 on plasma cells in the PB and BM of 7 matched samples. Intracellular expression was significantly higher in all PB samples compared with BM samples, with a median percentage expression of 31.6% (range, 12%-71%) in PB plasma cells compared with 5% (range, 0%-13.6%) in BM plasma cells (P = .001). (C) SDF-1 expression as measured by ELISA. SDF-1 level was markedly increased in the BM of MM patients (MM-BM; average, 6571 pg/mL) compared with healthy controls (CTRL-BM; average, 2632 pg/mL) (P < .001). In addition, the SDF-1 level in BM was significantly elevated compared with the SDF-1 level in PB of patients with MM (average, 2382.46 pg/mL) and in healthy control (MM-PB and CTRL-PB, respectively; P = .001). Error bars represent standard deviation; asterisks, statistically significant value.