KRAS and pancreatic ductal adenocarcinoma: Epithelial malignant cancer cells harbor “big 4” driver mutations, that is, substitutions or alterations of nucleotides in KRAS proto-oncogene, GTPase (KRAS), tumor protein P53 (TP53), and cyclin-dependent kinase inhibitor 2A (CDKN2A), and mothers against decapentaplegic homolog 4 (SMAD4) commonly occurs in pancreatic ductal adenocarcinoma (PDAC) (https://portal.gdc.cancer.gov), which can be useful for predicting survival in patients with resected PDAC (7).