CXCR4 and its ligand CXCL12 (also named stromal cell-derived factor 1, SDF-1) have been shown to be consistently expressed in human breast cancer cells, and the activation of SDF-1α/CXCR4 axis has found to play a key role in breast cancer migration and metastasis [10–12]. The gene discussed is CXCL12; the disease is breast carcinoma.