In PD-L1-positive metastatic melanoma and lung cancer, the efficacy of anti-PD-L1 antagonists is only 40%-50%; in colorectal cancer, although the PD-L1 positivity rate is as high as 50%, the efficacy of anti-PD-1 or anti-PD-L1 therapy is still not optimistic 38, 40-42; this is closely related to the complex tumor microenvironment. Here, PDCD1 is linked to metastatic melanoma.