CTLA4 and metastatic melanoma: The advent of immune checkpoint inhibition has revolutionised the treatment of cutaneous metastatic melanoma, with combined anti-programmed cell death protein 1 (anti-PD1) and anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) inhibitors resulting in 5-year survival rates of 50%, with 75% of survivors treatment-free [7,8].