CXCR4 and breast cancer: In addition, ectopic expression of CXCR4 in low metastatic HNSCC cells enables these cells to metastasize to regional lymph nodes, but not to the distant organs [44], whereas the ectopic overexpression of SDF-1 in CXCR4+ HNSCC and breast cancer cells enhanced in vitro cell motility and metastasis in lung [45, 46].