Precision medicine in head and neck cancer.

Head and Neck cancer is among the most common cancers worldwide, with a high prevalence in south East Asia, Brazil and central Europe. Head and Neck Squamous cell carcinoma (HNSCC) is associated with elevated mutational load but lacks specific genetic mutations. Exposure to carcinogens including tobacco and alcohol are the most dominant etiologic factors of HNSCC, while Epstein-Barr (HBV) and Human Papilloma Viruses (HPV) are associated with nasopharyngeal and oropharyngeal carcinoma, respectively. Surgery including open and minimally invasive procedures is considered the standard of care for the majority of oral cavity and early larynx cancers, while radiation therapy or concurrent chemoradiation are used for the other head and neck cancers. The treatment of patients with head and neck cancer is complex and has undergone considerable transformation in the last decade. These modalities include immunotherapy, targeted therapy (small molecule inhibitors or antibodies), or combined modality treatments. Emerging evidence supports a vital role of the immune system in eradicating HNSCC. Cancer cells express programmed death ligand 1 or 2 (PD-L1/2) which binds to the PD receptor on the T-cell, leading to an inactivation of the cytotoxic response of the T-cell. Cytotoxic T lymphocytes antigen-4 (CTLA-4) is another key player, expressed by cancer-activated T-cells, which binds to B7 ligand on the cancer cells, leading to inhibition of T-cells activation. Checkpoint inhibitors such as anti-PD-1 and anti-PD-L1 antibodies, were shown to significantly improve disease free survival and overall survival after failure of platinum-based chemotherapy. In addition, expression of HPV is associated with better response to single modality treatment (e.g. radiotherapy or surgery) and improved survival. In future years we expect to see the establishment of precision medicine modalities in an attempt to extend survival and improve quality of life of advanced stage HNSCC patients. Several phase III clinical trials are in progress to evaluate the utility of checkpoint inhibitors at different treatment settings, including combinations with adjuvant surgery, radiation therapy and chemotherapy.