CD274 and head and neck squamous cell carcinoma: The advent of immune checkpoint inhibitors (ICI) such as pembrolizumab, nivolumab, and avelumab, which target the interactions between programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) and PD-L2, opened new possibilities for combination therapies that might improve the outcomes of patients with locally advanced HNSCC.