CTLA4 and cancer: Immune checkpoint blockade (ICB) immunotherapy has provided significant clinical advances to combat a variety of cancers, which provokes an antitumor immune response via monoclonal antibodies (mAbs) against programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1) or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) 1.