The interaction between CXCR4 and CXCL12 mediates the progression and metastasis of breast and other cancers through a chemotactic effect; in the case of breast cancer, primary tumor cells overexpress CXCR4, whereas preferred organ sites of metastasis (lung, liver and bone) overexpress the CXCL12 ligand (3). This evidence concerns the gene CXCL12 and neoplasm.