CTLA4 and cancer: The past decade has seen multiple FDA approvals of tumor-specific immune system-activating therapies, generally referred to as cancer immunotherapy.1 2 These therapies range from immune modulators targeting programmed cell death protein 1 (PD-1), programmed death-ligant 1 (PD-L1), or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to cellular therapies using dendritic cells or genetically engineered T cells and monospecific or bispecific antibodies targeting tumor antigens.