The most common irAEs after checkpoint blockade are dermatologic (47%–65%), colitis (30%–48%), hepatitis (5%–30%) and/or endocrine (5%–10%) with different grades of severity.229,230 Interestingly, irAEs are more frequent in cancer patients upon anti-CTLA-4 (60%–85%, mostly grades 1 and 2) than anti-PD-1 (16%–37%, with a minority of patients displaying high-grade toxicity) blockades.229,231–233 Environmental factors have been shown to influence the occurrence of irAEs. This evidence concerns the gene CTLA4 and colitis.