In the mice model of pancreatic ductal adenocarcinoma (PDA), Feig et al. noticed ineffectiveness of checkpoint inhibitors targeting anti-cytotoxic T-lymphocyte-associated protein 4 (α-CTLA-4) and α-programmed cell death 1 ligand 1 (PD1-L1). This evidence concerns the gene CTLA4 and Patent ductus arteriosus.