CXCR4 and breast cancer: Blocking CXCR4 may attenuate breast cancer metastasis to regional lymph nodes and the lungs [7], and activation of CXCR4 is believed to be primarily ligand-dependent, as is supported by the antitumor efficacy of AMD 3100, an antagonist of chemokine (C-X-C motif) ligand 12 (CXCL12) binding [8].