The molecular mechanisms by which CXCR4 promotes tumor growth have been widely studied and are summarized as follows: (1) CXCL12 produced in the tumor microenvironment allows the entrance of circulating endothelial progenitor cells to the primary tumor site and produces additional microvessels, thereby increasing the oxygen supply to the tumor14,94. This evidence concerns the gene CXCL12 and neoplasm.