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. Yervoy 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. Yervoy binds to a substance called CTLA-4, which is found on T cells (a type of white blood cell). Yervoy 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 ipilimumab and MDX-010.