CXCL12 and cancer: CXCR4 and CXCR7 represent two cognate receptors for CXCL12.251–253 Both CXCR7 and CXCL12 are highly expressed on certain cancer cells.254,255 CXCL12 can also be detected in normal tissues such as blood vascular endothelial cells,255,256 and fibroblasts are probably a major source of CXCL12 secretion in tumor tissue.257,258 Initially shown to facilitate the mobilization of hematopoietic stem cells and create a microenvironment for cancer stem cells,259 CXCL12/CXCR4 pathway signaling also plays an important role in cancer cell proliferation and angiogenesis.259,260