The role of chemokine receptors in metastatic organ selectivity was first reported for CXCR4, a receptor that stimulates metastasis of breast cancer and melanoma cells to the lung and lymph node where its ligand, CXCL12 (also known as SDF-1: stromal cell-derived factor 1), is abundant [5]. This evidence concerns the gene CXCL12 and breast carcinoma.