PDCD1 and head and neck squamous cell carcinoma: Evaluation of anti-PD-1 treated R/M HNSCC patients showed lower intratumoral hypoxia was associated with increased efficacy and was independently associated with clinical benefit rate and PFS in multivariate analysis, which included tumor infiltrating CD8 T cells, the latter of which has also shown predictive value with anti-PD-1 mAb therapy (81, 82).