PDCD1 and head and neck squamous cell carcinoma: PD-1/PD-L1 monoantibodies, such as nivolumab, pembrolizumab, and atezolizumab, have already been approved by the Food and Drug Administration (FDA) for the treatment of melanoma, non-small cell lung cancer (NSCLC), head and neck squamous cell carcinoma (HNSCC), urothelial cancer, and more than 10 other cancers.