CXCL12 and neoplasm: Similarly, several secreted factors, such as vascular endothelial growth factor (VEGF) [6], stromal cell-derived factor-1 (SDF-1) [5], Chemokine (C-C motif) ligand 5 (CCL5) [14], Chemokine (C-C motif) ligand 2 (CCL2) [15] and matrix metalloproteinase 9 (MMP9) [1], have been implicated as possible regulators for enhancing tumor growth.