CXCR4 and breast neoplasm: In addition to what has been discussed above, it has also been suggested that delivery of CXCL12 to chemotherapy-induced dormant neuroblastoma cells led to down-regulation of genes associated with cell quiescence [294], and dormant breast tumor cells in lung metastatic sites had reduced CXCR4 expression [295], reinforcing the role CXCL12/CXCR4 signaling may play in reanimation of dormant tumor cells in metastatic sites.