PDCD1 and pancreatic ductal adenocarcinoma: Concomitant inhibition of TGF-β receptor I and PD-1 synergistically represses tumor promotion in a genetically engineered mouse model of pancreatic ductal adenocarcinoma, and clinical studies using a combination of TGF-β blockers and PD-1/PD-L1 inhibitors are currently underway [35,48].