CTLA4 and metastatic melanoma: The concept to target immune cells rather than cancer cells has achieved unexpected success especially with monoclonal antibodies against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death protein (PD-1) and its ligand PD-L1, improving enormously the survival rates of patients with metastatic melanoma, lung, renal, and urothelial cancers (2).