CXCL12 and central nervous system cancer: The hypoxia-inducible factor (HIF), a master transcription factor that regulates hypoxia, also promotes expression of stromal cell-derived factor-1 (SDF-1), vascular endothelial growth factor (VEGF) and urokinase plasminogen activator (uPA) in glioma cells, which is also critical in determining neural stem cells’ (NSCs’) tropism towards glioblastoma tumors, while antibody-mediated blocking of their cogent receptor signaling significantly abolished their tumor-tropic behavior [49,50].