Recurrent/ Metastatic Olfactory Neuroblastoma

This trial evaluates the efficacy and safety of nivolumab monotherapy in patients with recurrent or metastatic olfactory neuroblastoma that is difficult to treat with curative intent. Specifically, nivolumab 240 mg will be administered on Day 1 and Day 15 of each cycle, or nivolumab 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 their attending physician.