CXCL12 and neoplasm: CAFs promote angiogenesis through activation of the tumor-derived proangiogenic growth factors, platelet-derived growth factor (PDGF), VEGF, FGF, and transforming growth factor-beta (TGF-β), and by secreting stromal cell-derived factor-1 (SDF-1), which draws endothelial progenitor cells to the tumor stroma [138].