PDCD1 and head and neck squamous cell carcinoma: The KEYNOTE‐040 study (a randomized phase III trial that investigated the role of pembrolizumab vs. conventional treatment) showed that pembrolizumab, a humanized monoclonal antibody targeting PD‐1, prolonged median overall survival (OS) time and was therefore preferred over conventional treatment as a second‐line agent for treatment of R/M HNSCC.3