A drug used alone or with ipilimumab to treat a certain type of colorectal cancer that has mutations (changes) in genes involved in DNA repair. It is also used with ipilimumab in some patients to treat renal cell carcinoma (RCC) and melanoma. Nivolumab is also used alone in some patients to treat small cell lung cancer, non-small cell lung cancer, cancer of the head and neck, Hodgkin lymphoma, melanoma, RCC, urothelial carcinoma, and hepatocellular carcinoma. It is also being studied in the treatment of other types of cancer. Nivolumab binds to a protein called PD-1, which is found on T cells (a type of white blood cell). Nivolumab may block PD-1 and help the immune system kill cancer cells. It is a type of monoclonal antibody and a type of immune checkpoint inhibitor. Also called Opdivo.