PDCD1 and head and neck squamous cell carcinoma: The United States Food and Drug Administration (US FDA) has approved antibodies targeting the PD1–PD‐L1 axis as first‐line or second‐line therapies for a number of cancers, including melanoma, lung cancer, lymphoma, head and neck squamous cell carcinoma (HNSCC), renal cell cancer (RCC), gastro‐oesophageal cancer, and liver cancer.15