CSF2 and head and neck squamous cell carcinoma: About 50–60% of HNSCC patients express PD-L1, which is induced by the inflammatory environment in TME—the presence of interferon-gamma (IFN-γ), tumour necrosis factor-alpha (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL) 4 [15,18,23,36,38].