CTLA4 and cancer: In patients with advanced melanoma or renal cell carcinoma (RCC), treatment with CPI targeting programmed cell death protein 1 (PD1) (e.g. nivolumab, pembrolizumab) as monotherapy or in combination with anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4) (ipilimumab with nivolumab) are now established as standard of care.[1], [2], [3] With their adoption as an effective therapy for advanced cancers, a range of immune-related adverse events (irAE) affecting different organs have also emerged.