CXCL12 and breast cancer: The causative effects of intratumor CXCL12 are suggested by the epigenetic silencing of the CXCL12 promoter, which resulted in high metastatic potential in breast cancer cells [21], while the re-expression of CXCL12 in highly aggressive mammary carcinoma cell lines limited metastatic progression in mouse xenograft models [21].