PDCD1 and cancer: Subsequently, the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed on these 841 genes, and the results demonstrated that the target genes were enriched in the Apoptosis, PD-L1 expression and PD-1 checkpoint pathway in cancer, mitogen-activated protein kinase (MAPK) signaling pathway, and Ras signaling pathway (Fig. 5B).