TGFB1 and pancreatic ductal adenocarcinoma: Among them, TGF-β/Smad pathway is acknowledged holding a key position in cancer stem cells, and reported there is a dual directional regulation mechanism with microRNAs: TGF-β could induce epithelial-to-mesenchymal transition (EMT) and stemness in pancreatic ductal adenocarcinoma via induces miR-100 and miR-125b but blocks let-7a (7); meanwhile, TGF-β pathway could also be regulated by microRNAs: TrkC-miR2 and miR-140 inhibit TGF-β pathway via direct targeting smad3 (8, 9).