Therefore, the T-cell receptor signaling pathway (hsa04660) was further analyzed, revealing that neither PDCD1 (PD-1) nor CTLA4, the ICIs target ligands, were upregulated in HNSCC, as also confirmed by ST (Fig. 4d, Online Resource 7) and SIN (data not shown) compared with NOM. This evidence concerns the gene CTLA4 and head and neck squamous cell carcinoma.