NGF and neoplasm: Cumulative evidence shows that tumors and surrounding tissue cells release various algogenic substances, including protons, proteases, endothelins, vascular endothelial growth factor (VEGF), nerve growth factor (NGF), and transforming growth factor–β (TGF-β), in the tumor microenvironment to sensitize and injure primary sensory neurons (10, 14, 38–41).