A drug used with nivolumab to treat a certain type of colorectal cancer that has mutations (changes) in genes involved in DNA repair. It is also used with nivolumab in some patients to treat advanced renal cell carcinoma that has not already been treated. Ipilimumab is also used alone to treat melanoma that cannot be removed by surgery or has spread to other parts of the body. It is also used as adjuvant therapy to treat melanoma in the skin and lymph nodes in patients who have already had surgery. It is also being studied in the treatment of other types of cancer. Ipilimumab binds to a substance called CTLA-4, which is found on T cells (a type of white blood cell). Ipilimumab may block CTLA-4 and help the immune system kill cancer cells. It is a type of monoclonal antibody and a type of immune checkpoint inhibitor. Also called MDX-010 and Yervoy.