CXCL12 and neoplasm: Despite the discrepancies in their reported contributions to the composition of tumor vasculature, these cells can contribute to neovascularization by virtue of their production of pro-angiogenic mediators including VEGF, insulin-like growth factor (IGF)-1, angiopoitin (Ang)-1 and -2, and CXCL12/stromal cell-derived factor-1/SDF-1 (Ahn and Brown, 2009).