CTLA4 and metastatic melanoma: Over the past few years, emerging immune checkpoint inhibitors (ICIs), such as anti-PD-L1 (programmed cell death ligand 1) and anti-CTLA-4 (cytotoxic T-lymphocyte antigen4), have presented significant clinical efficacy and observably improved the treatment of the unresectable and metastatic melanoma as well as those with a high risk of recurrence after resection [2, 37–39].