PDCD1 and cancer: A detailed discussion based on in vitro and in vivo studies examining the influence of various natural compounds on PD-1/PD-L1 in cancer is presented in Tables 3 [219–248] and 4 [220, 222, 224, 226, 227, 230–232, 235–237, 240, 241, 243, 244, 246, 247, 249–254], respectively.