GDNF and neoplasm: The detection of increased neurotrophic factors such as nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), neural cell adhesion molecules (NCAMs), myelin-associated glycoprotein (MAG), and chemokines in intrapancreatic nerves and tumor cells and their receptors on tumor cells led to an increased attention to these molecules in recent years [96–98].