PDCD1 and head and neck squamous cell carcinoma: Programmed cell death 1 (PD‐1) signaling and its ligand PD‐L1 are classical immune checkpoints, and related inhibitors have achieved immense success in clinical trials.[99] A clinical trial reported that PD‐1/PD‐L1 inhibitors could be potential radiosensitizers in head and neck squamous cell carcinoma,[100] and Liu et al.