CXCR4 and neoplasm: We have previously demonstrated that CXCL12 is expressed in normal epithelial cells in intestine and mammary glands, but is epigenetically silenced in human breast and colorectal cancer [24], [25].This pattern of CXCL12 gene repressionresults in tumor cells whose chemokine – receptor profilesmirror that of highly mobile leukocytes, which express the receptors CXCR4 and CXCR7 but not the ligand.