PDCD1 and cancer: Emerging evidence indicates that existing immune checkpoint inhibitors, such as anti-PD-1, anti-PD-L1, and anti-CTLA4 antibodies, can be effective monotherapies for immune-sensitive cancers, including NSCLC and malignant melanoma [11,12], but they lack efficacy in the case of pancreatic cancers [2,3,4,5,6,7,8,9,10,13,14,15,16,17,18].