Drugs targeting CTLA4 and the PD1 pathway have since been applied to a wide range of tumor types including lymphoma, lung cancer, renal cell carcinoma (RCC), head and neck squamous cell carcinoma (HNSCC), bladder cancer, liver cancer, breast cancer, and gastro-esophageal cancer (37). This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.