In the past few decades, immunotherapy has been the focus of cancer research and various methods have emerged to treat cancers, such as immune checkpoint inhibitors (ICI) against the programmed cell death protein-1 (PD-1) or its ligand (PD-L1) and cytotoxic T lymphocyte associated antigen-4 (CTLA-4), vascular endothelial growth factor (VEGF) inhibitors, cytokines, vaccines, and adoptive cellular therapy (ACT). Here, CTLA4 is linked to cancer.