Inclusion criteria: (a) Diagnosed with head and neck squamous cell carcinoma, including mucosa of oral cavity, larynx, or pharynx, (b) RCTs, and (c) Anti-PD1/PD-L1 inhibitors as interventional therapies, while the other group may have received standard therapy and/or ICI combination therapy. Here, PDCD1 is linked to head and neck squamous cell carcinoma.