Although targeting immune checkpoints such as programmed cell death protein 1 (PD‐1) and its ligand, programmed cell death ligand 1 (PD‐L1), or cytotoxic T lymphocyte‐associated antigen‐4 (CTLA‐4) has achieved noteworthy benefit in multiple cancers by blocking immunoinhibitory signals and enabling effective antitumor responses,[45, 46] limited responses to these immunotherapies were reported in patients with metastatic breast cancer, emphasizing the need to identify strategies that will increase response efficacy. Here, CTLA4 is linked to cancer.