PDCD1 and head and neck squamous cell carcinoma: In 2016, two anti-PD-1 checkpoint inhibitor monoclonal antibodies (mAbs), pembrolizumab and nivolumab provided new options for cisplatin resistant recurring or metastatic HNSCC following accelerated FDA approval based on encouraging clinical trial data (16, 17) and precedence of response efficacy in large phase III clinical trials of melanoma and non-small cell lung cancer in which both antibodies had already demonstrated significant improvements in patient outcomes compared to current standard of care therapy (4, 5, 18, 19).