CXCR4 and cancer: CXCL12 exerts its function by binding to the seven-transmembrane G-protein-coupled receptor CXCR4 and CXCR7, which were expressed on a great diversity of cell types, including lymphocytes, hematopoietic stem cells, endothelial cells, epithelial cells, stromal fibroblasts, and cancer cells [9].