The clinical successes and Food and Drug Administration (FDA) approvals of the immune checkpoint inhibitors (ICIs) ipilimumab (Yervoy®, 2010), pembrolizumab (Keytruda®, 2016), and atezolizumab (Tecentriq®, 2016) targeting Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4), Programmed cell Death protein 1 (PD-1), and programmed death-ligand 1 (PD-L1), respectively, have highlighted the relevance of addressing tumor evasion mechanisms in the management of cancer. Here, CTLA4 is linked to cancer.