GDNF and familial pancreatic carcinoma: Furthermore, Nodal, a protein playing a role in the activation of the differentiation process of embryonic tissues and neural development during embryogenesis (146), has been shown to influence the expression of NGF, BDNF, GDNF, and MMP-9, resulting in the enhancement of pancreatic cancer cell invasion ability, dorsal root ganglia (DRG) and synapse outgrowth, and hence the promotion of PNI (130).