CXCR4 and neoplasm: Studies on the CXCR4/CXCL12 axis have shown that CXCL12 is highly secreted by regional lymph nodes, lung, liver and marrow, and that CXCL12 can stimulate CXCR4-expressing tumor cell motility and invasiveness.14 Meanwhile, CXCL12 in tumor microenvironments can also induce the recruitment of endothelial progenitors for tumor angiogenesis.23 To determine the effect of E5 on the chemotaxis of 4T1 cells in response to CXCL12 and MS-5 conditional medium, the transwell assay was performed.