This clinical trial has established head and neck squamous cell carcinoma as responsive to immunotherapy and nivolumab as a new potential SOC for these patients. As concern safety, high-grade (CTCAE v4.03 Grade 3 or higher), treatment-related, select adverse events occur with a low frequency in patients with Recurrent or Metastatic Platinum-refractory Squamous Cell Carcinoma of the Head and Neck (SCCHN) treated with nivolumab monotherapy. Nonetheless, this observation arises from patients treated in clinical trial and selected according to clear inclusion and exclusion criteria. Therefore they may not precisely reflect the clinical practice. Using a single large study is warranted in order to expand the safety database and to improve the knowledge on estimated incidence of uncommon, select, high-grade AEs.