Muller and colleagues have shown that chemokine receptors CXCR4 and CXCR7 are highly expressed in human breast cancer specimens, while their corresponding ligands CXCL12/SDF-1alpha (stromal cell-derived factor) and CCL21/6Ckine showed peak levels in primary breast cancer destination sites [20]. Here, CXCR4 is linked to breast cancer.