CD274 and head and neck squamous cell carcinoma: One of the most widely studied predictive molecular biomarkers in PD‐1 and PD‐L1 immunotherapy is the level of expression of PD‐L1, which has previously been shown to correlate with survival outcomes in a variety of other cancers, including melanoma, non‐small cell lung cancer and head and neck squamous cell carcinoma.34, 35