FOXO1 and neoplasm: PAX3-and PAX7-FKHR gene fusion [24], mutations in the von Hippel Lindau gene [25], hypoxic conditions in the tumor microenvironment [26], NF-κB [21], vascular endothelial growth factor [27], and tumor necrosis factor alpha [28] have all been found to regulate CXCR4 overexpression in different tumor cells.