CXCR4 and neoplasm: EPCs are mobilized from the bone marrow by the cytokine stromal-derived factor-1α (SDF-1α) [45] that is expressed by angiogenic vessels in GBM, SDF1α binds to the G protein-coupled chemokine 4 receptor (CXCR4) expressed on circulating EPCs and also on tumor vessels [46].