PDCD1 and lung adenocarcinoma: A previous report founds that hsa_circ_0000519 (circ_0000519, also named hsa_circ_002178) is an upregulated circRNA in lung adenocarcinoma, as revealed by the GSE101684 and GSE101586 datasets, and it can be transferred by exosomes to be involved in immune therapy by regulating programmed death-ligand 1 (PDL1)/programmed cell death protein 1 (PD1) [14].