Nivolumab With or Without Ipilimumab in Treating Patients With Refractory Metastatic Anal Canal Cancer

This phase II trial studies how well nivolumab with or without ipilimumab works in treating patients with anal canal cancer that has not responded to previous treatment (refractory) and that has spread from where it first started (primary site) to other places in the body (metastatic). Immunotherapy with monoclonal antibodies, such as nivolumab and ipilimumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread.