Immune checkpoint inhibitors (ICIs), including programmed cell death protein 1 (PD-1) inhibitors, such as nivolumab, and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors, such as ipilimumab, have revolutionized cancer treatment, particularly in metastatic melanoma. This evidence concerns the gene CTLA4 and metastatic melanoma.