PDCD1 and head and neck squamous cell carcinoma: The advent of immune checkpoint inhibitors (ICIs) targeting PD-1/PD-L1 (e.g., pembrolizumab, nivolumab) and CTLA-4 (e.g., tremelimumab) has revolutionized HNSCC management, offering durable responses in a subset of patients by reactivating antitumor immunity [11–13].