A number of functional studies investigating the influence of CXCR4 expression and activation by its ligand CXCL12 have recently been performed, revealing that CXCR4-CXCL12 axis plays an important role in regulating metastasis of breast cancer to specific organs [23, 25, 34, 35]. The gene discussed is CXCR4; the disease is breast carcinoma.