CTLA4 and cancer: Recently, cancer immunotherapy using immune‐checkpoint blockade (ICB) that targets programmed cell death 1 (PD‐1), programmed cell death‐ligand 1 (PD‐L1), programmed cell death‐ligand 2 (PD‐L2) and cytotoxic T‐lymphocyte‐associated protein 4 (CTLA‐4) provides significant clinical benefits in cancer.33