In agreement with previous findings showing that CXCL12 is preferentially expressed in the most common metastatic sites of BC (i.e., the LNs, lung, liver, and bone marrow) and that it induces the recruiting of CXCR4-positive cancer cells to CXCL12-expressing sites, our results suggest that the chemokine CXCL12 and its cognate receptor CXCR4 exert a key role in determining the metastatic potential of breast tumor cells [30, 33]. This evidence concerns the gene CXCR4 and breast cancer.