A drug used to treat melanoma that has spread to other parts of the body or that cannot be removed by 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 the surface of 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. Also called ipilimumab and MDX-010.