CXCR4 and breast cancer: Further studies are required to clarify the role of CXCR4 in predicting organ specificity in breast cancer metastasis; to explain whether CXCR4 could change in the process of breast cancer neoadjuvant therapy and whether this change could be significant for treatment and prognosis; and to evaluate the application of CXCR4 as a bio-marker for breast cancer prognosis and target therapy.