KRAS and pancreatic ductal adenocarcinoma: Instead, its expression is regulated by transforming growth factor (TGF)-β in A549 cancer cells and by epidermal growth factor receptor/KRAS-ERK signaling pathways in pancreatic ductal adenocarcinoma (PDAC) (Keshamouni et al., 2006; Yu et al., 2008; Dhiraj and Lowenfels, 2013; Sun et al., 2018).