GDNF and cancer: This idea is supported by the upregulation of neuronal receptors such as AMAPR, NMDAR, GFRα1, GFRα2, GFRα3, AChR, L1-CAM, and NCAM and their ligands, including glutamine, GDNF, NRTN, ARTN, and Ach, in cancers (Figure 3).