CCL2 and central nervous system cancer: Endothelial cell growth factor (EGF), platelet-derived growth factor (PDGF), VEGF, TGF-β1, interleukin (IL)-8, SDF-1α and monocyte chemoattractant protein-1 (MCP-1) are found to be secreted by stromal cells or glioma cells, contributing to the tumor-tropic effects of MSCs [69,70,71].