Emerging evidence has revealed that C-X-C chemokine receptor 4 (CXCR4), a 352 amino acid rhodopsin-like G-protein-linked receptor, is overexpressed in many different types of human cancers, including osteosarcomas [5], glioma [6], prostate cancer [7], breast cancer [8] and colorectal cancer [9]. Here, CXCR4 is linked to breast cancer.