In the era of cancer immunotherapy, immune checkpoint inhibitors (ICIs) targeting cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or its ligand (PD-L1) are used across various cancer types in clinical trials and in practice.1 However, atypical patterns of response, such as pseudoprogression and hyperprogressive disease (HPD), have been observed in cancers treated with ICIs.2,3. The gene discussed is CTLA4; the disease is cancer.