RPIA and pancreatic ductal adenocarcinoma: Naiara et al. found in an experimental model of pancreatic ductal adenocarcinoma (PDAC) that the proto-oncogene K-RAS could activate mitogen-activated protein kinase (MAPK), leading to an increase in the expression of the oncogene MYC and finally increasing the transcriptional activity of ribose 5′-phosphate isomerase A (RPIA), a raw material necessary for nucleotide metabolism, in the nonoxidative pentose phosphate pathway (PPP) [73].