PDCD1 and cancer: The KEGG enrichment analysis of the DEGs revealed that the immunoregulatory pathways (e.g., natural killer cell-mediated cytotoxicity, Th17 cell differentiation, Th1 and Th2 cell differentiation, T-cell receptor signaling pathway, and PD-L1 expression and PD-1 checkpoint pathway in cancer) were significantly over-presented (Figure 5B), which was extremely similar to the functionality of the PRs (Figure S2A).