Clinical significance of the tumor microenvironment of the head and neck squamous cell carcinoma

The biological significance of the tumor microenvironment is now evident in shaping the behavior of the tumors and the outcome of the disease. Previously extracellular matrix components were widely studied in head and neck cancers but clinically useful biomarkers have not been developed. The vascularization of these cancers is unique and non-neoangiogenic; accordingly, the anti-angiogenic agents are not active in this tumor type. However, these tumors are typically hypoxic, have elevated VEGF expression, contributing to the ”immunosuppressive” microenvironment. Tumor cell expression of PD-L1, and loss of HLA expression are also strong contributors to the immunosuppressive microenvironment. CD8+ T-cell density seems to be a useful prognostic marker of this tumor type. Furthermore, this biomarker is also a predictive one for the efficacy of immunotherapies beside the well-known stromal cell PD-L1 expression.