CTLA4 and metastatic melanoma: The first checkpoint inhibitor against cytotoxic T lymphocyte protein 4 (CTLA-4, CD152, ipilimumab; Bristol-Myers Squibb; interacts with CD80 (B7.1), alternatively with CD86 (B7.2)) has been approved in March 2011 in the US for the treatment of patients with unresectable or metastatic melanoma [1].