Intra-tumoral and peripheral PD-1/PD-L1 expression correlation in head and neck cancer

Background Head and neck squamous cell carcinoma (HNSCC) represents a heterogeneous group of malignant disease of the oral cavity, pharynx and larynx. HNSCC cells evade the immune system through alterations in their immunogenicity, production of immunosuppressive mediators, and induction of immunomodulatory cell types. The immune status of solid HNSCC can be considered as hot, cold or excluded based on the distribution of tumor infiltrating immune cells. In this context immunotherapies via blockade of checkpoint molecules programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) have significantly improved therapeutic outcomes in different cancer types. In HNSCC, intra-tumoral expression levels of PD-L1 are used for decision making in checkpoint inhibitor treatment. The significance of PD-L1 as a prognostic indicator is still controversial because both PD-1 and PD-L1 are also expressed in different types of circulating immune cells and the interaction of systemic and intra-tumoral cell-type-specific expression patterns of checkpoint molecules PD-1/PD-L1 has not yet been fully understood.