CTLA4 and metastatic melanoma: Immune checkpoint inhibitors, in particular anti-PD-1 antibodies such as pembrolizumab and nivolumab and the combination of nivolumab with the anti-CTLA-4 antibody ipilimumab, can achieve long-term survival for patients with metastatic melanoma with 5 year survival rates of more than 40% and 50%, respectively.