CXCL12 and cancer: Microvessel density was found to be higher in the stroma of NPC tissues as was the presence of CXCR4-positive and CD133/VEGFR-2-double-positive cells, indicating the presence of endothelial progenitor cells in both NPC cancer and stromal cells to enhance neoangiogenesis in a VEGF- and SDF-1 dependent manner.