Turning the tide: Clinical utility of PD-L1 expression in squamous cell carcinoma of the head and neck.

The use of cytotoxic and/or targeted agents is the gold standard in first- and second-line treatment of metastatic head and neck cancer. Currently the focus of oncologic research is shifting to the implementation of immune checkpoint inhibitor regimens. Many trials are being performed evaluating the survival benefit of various PD-1/PD-L1 blocking antibodies in both solid and haematological malignancies. Also, evaluation of the predictive value of PD-L1 expression on tumour cells and immune cells is being explored. We first review the current knowledge and possible pitfalls for PD-L1 expression in squamous cell carcinoma of the head and neck. Next, we provide an update on the therapeutic use of PD-1/PD-L1 blocking antibodies as treatment modality for patients with squamous cell carcinoma of the head and neck and we assess the predictive value of tumour PD-L1 positivity. Finally, we elaborate on other promising predictive biomarkers of interest in this patient population.