Gastrointestinal tract toxicity, on the other hand, is pervasive in patients with melanoma, and lower gastrointestinal toxicity (i.e., ICI colitis) is prevalent with the use of anti-CTLA4 agents (i.e., 10–25% incidence) compared with anti-PD1 ICI (i.e., 1–5%) and, finally, with a considerable incidence when combination therapy is considered (i.e., about 20%) [34]. This evidence concerns the gene CTLA4 and colitis.