Although colitis is the most common irAE in patients treated with anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) antibodies, the rate of grade 3/4 diarrhea in those given PD-1/ programmed cell death ligand 1 (PD-L1) agents is very low (1 to 2%) [4–6]. This evidence concerns the gene PDCD1 and colitis.