PDCD1 and cancer: PD-1 inhibitors, such as nivolumab and pembrolizumab, have been evaluated in a number of cancer types, and several PD-1 inhibitors are now approved as monotherapy and in combination with other anticancer agents in multiple cancers, including head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) [7–9].