Ipilimumab (Yervoy, Bristol-Myers Squibb Company), which functions by inhibiting the co-inhibitory receptor CTLA-4, was the first immune checkpoint inhibitor (ICI) found to extend survival in metastatic melanoma, leading to its FDA approval for the treatment of melanoma in 2011 [32,35]. The gene discussed is CTLA4; the disease is metastatic melanoma.