Since 2011, the FDA approved six ICIs—ipilimumab (anti-CTLA-4), nivolumab (anti-PD-1), pembrolizumab (anti-PD-1), atezolizumab (anti-PD-L1), avelumab (anti-PD-L1), and cemiplimab (anti-PD-1)—for the treatment of more than 15 different types of cancer [63]. This evidence concerns the gene CTLA4 and cancer.