CCL2 and central nervous system cancer: SDF-1α, VEGF, platelet-derived growth factor (PDGF), endothelial cell growth factor (EGF), TGF-β1, interleukin (IL)-8, and monocyte chemoattractant protein-1 (MCP-1) have been found to be secreted by glioma cells or stromal cells and to contribute to tumour-tropism of MSCs [12–14].