CTLA4 and cancer: Immune checkpoint inhibitors for cytotoxic T lymphocyte antigen 4 (CTLA4) or the programmed cell death protein 1 (PD1) pathway have achieved impressive success rates in the treatment of various types of malignancies.[1, 2] However, the response rates of patients to anti‐CTLA4 and anti‐PD‐1 treatments remain low in many cases, leading to studies of other immune checkpoints.[3, 4] A better understanding of checkpoint molecules may support the development of next‐generation cancer immunotherapies.