PDCD1 and head and neck squamous cell carcinoma: In recent years, immunotherapies, particularly programmed cell death 1 (PD-1) inhibitors, have emerged as a promising area of research, showing the ability to improve OS in patients with PD-1 ligand 1 (PD-L1)-positive recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) 11.