The discovery of immune checkpoint proteins, such as CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), PD-1 (programmed death-1), TIM-3 (T-cell immunoglobulin and mucin-domain containing-3), LAG-3 (Lymphocyte-activation gene 3), and IDO (Indoleamine 2,3-dioxygenase), along with a better understanding of the role that they play in the mechanisms of immune evasion in tumors have facilitated the production of a significant anti-tumor immune response in patients with cancer. Here, CTLA4 is linked to cancer.