CTLA4 and cancer: Immune checkpoint inhibitors (ICIs) act by activating the immune system to eliminate cancer cells by targeting one of the following checkpoints: programmed death-1 (PD-1) as well as its ligand (PD-L1) as in the case of durvalumab, the lymphocyte activation gene 3 (LAG3), and the cytotoxic T-lymphocyte associated protein 4 (CTLA-4) [36].