The aims of this study were to investigate (i) whether S100A8/A9 expression in tissue sections of primary melanomas and melanoma metastases discriminates between short-term and long-term survivors, (ii) whether elevated serum S100A8/A9 is associated with impaired survival of stage III and IV melanoma patients, and (iii) whether elevated serum S100A8/A9 is associated with survival of melanoma patients treated with the anti-PD-1 immune checkpoint inhibitor pembrolizumab. This evidence concerns the gene PDCD1 and melanoma.