Recurrent/Metastatic Olfactory Neuroblastoma: Evaluating the Efficacy and Safety of Nivolumab

240 mg will be administered on Day 1 and Day 15 of each cycle, or 480 mg will be administered on Day 1 of each cycle, and this will be continued until disease progression. One cycle is 28 days. The decision on which treatment to administer will be made through consultation between the participant in this trial and the site principal investigator or site co-investigator.