The researchers suggest that CXCR4 is downregulated in metastasized cancer cells depending on the favorable change of the environment that induces dormancy to cancer cells, although not dependent on the expression level of CXCL12 in lung tissue [45] In addition, lower levels of CXCL12 in PT were also observed in human breast cancer. This evidence concerns the gene CXCL12 and breast cancer.