CXCL12 was shown to transactivate HER2-neu in the breast cancer cell lines MDA-MB-361 and SKBR3, which express both CXCR4 and HER2-neu that was inhibited by AMD3100, a CXCR4 inhibitor, PKI 166, an epidermal growth factor receptor/HER2- tyrosine kinase inhibitor, and PP2, a Src kinase inhibitor. The gene discussed is CXCL12; the disease is breast cancer.