CXCR4 and breast cancer: Breast cancer metastasis is promoted by a number of factors, including signaling from the stromal cell-derived factor 1 (SDF-1) to the CXC Receptor 4 (CXCR4), and mutations in the TP53 gene in combination with the upregulation of Mouse Double Minute 2 and 4 (MDM2 and MDM4).