PDCD1 and cancer: KEGG pathway enrichment analysis indicated that immune-associated pathways were highly enriched in the Immunity_H subgroup in both GSE62254 and GSE29272, which included primary immunodeficiency, antigen processing and presentation, the B cell receptor signaling pathway, chemokine signaling, natural killer cell-mediated cytotoxicity, the Toll-like receptor signaling pathway, PD-L1 expression and the PD-1 checkpoint pathway in cancer (Fig. 3C, E).