SMAD4 and pancreatic ductal adenocarcinoma: Among the various types of pancreatic cancer, pancreatic ductal adenocarcinoma is the type of pancreatic cancer with the highest incidence, the highest aggressive and the highest mortality rate; when KRAS is mutated, the oncogenes occur in the order of CDKN2A, TP53 and SMAD4, culminating pancreatic ductal adenocarcinoma [82, 83].