CTLA4 and cancer: Inhibition of the cytotoxic T-cell response is one of the main mechanisms used by cancer cells to evade the immune system and is mediated by several factors, such as the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), the programmed death receptor 1 (PD-1) and its ligand PD-L1, whose inhibition with ICIs constitutes one of the recent revolutions in cancer treatment [24,25].