CD274 and head and neck squamous cell carcinoma: This systematic review and meta-analysis of 17 studies19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35 found that high PD-L1 expression levels on immune cells in the tumor immune microenvironment were associated with extended OS and specific survival in patients with localized and locoregionally advanced HNSCC.