Interestingly, evaluating intracellular expression of CXCR4 in myeloma PCs from BM biopsy specimens, we found higher intracellular CXCR4 levels in CD138+ cells of patients who failed to respond to BTZ compared with patients who responded, indicating that CXCR4 may influence response to chemotherapy in MM patients. Here, CXCR4 is linked to plasma cell myeloma.