PDCD1 and head and neck squamous cell carcinoma: Differential gene expression analysis between responders and non-responders to anti-PD1/PD-L1 immunotherapy will focus on immune-related genes such as immune checkpoint genes, but also on genes that play important roles in TME including hypoxia-related genes, ΔNp63 (potentially implicated in the recruitment of myeloid-derived suppressor cells and overexpressed in HNSCC), immunogenic cell death genes, and mitophagy-related genes, which may be targeted to improve the effectiveness of cancer immunotherapy [33–35].