CXCR4 and breast cancer: Plerixafor (also termed as AMD3100), a CXCR4 commercial antagonist, has been approved by the FDA for hematopoietic stem cell mobilization as an injectable agent for short-term treatments,9,10 and it was able to block CXCR4 activation to inhibit metastasis of multiple solid tumors such as breast cancer,11 glioblastoma12 and melanoma.13 Moreover, AMD3100 increased the efficiency of multiple chemotherapeutics against leukemia, breast cancer, prostate cancer and glioma.7,14 Peptide T140 and its analogs blocking CXCR4 in vitro and in vivo have also been documented in numerous preclinical studies.