CXCL12 (also known as stromal cell-derived factor 1 (SDF-1)) is expressed by a variety of cells of the bone microenvironment including osteoblasts and endothelial cells [39] while cancer cells including breast cancer cells express CXCR4 [40], the receptor for CXCL12. The gene discussed is CXCL12; the disease is breast cancer.