PDCD1 and head and neck squamous cell carcinoma: These findings suggest that the immune response to PD-1 inhibitors may be related to the presence of an acquired immune response following INF-γ production in a variety of cancers, including advanced melanoma, head and neck squamous cell carcinoma (HNSCC), anal canal, biliary, gastrointestinal, colon, esophageal, and ovarian cancers (54).