CXCR4, a cell surface chemokine receptor, binds and responds to cytokines of the CXC chemokine family such as a CXCL12 (or SDF-1), and it has a wide cellular distribution including lymphocytes, hematopoietic stem cells, endothelial and epithelial cells, and cancer cells [72]. Here, CXCL12 is linked to cancer.