One of our patients received another anti‐CTL4 antibody, tremelimumab, but its role is difficult to assess; the drug was associated with an OX40 agonist: even if the adverse effects of this compound are not well known, OX40 stimulation is known to be experimentally colitogenic34; moreover, the patient also received daily lansoprazole: this proton pump inhibitor is definitely associated with an increased risk of collagenous colitis.5 The gene discussed is SLC44A4; the disease is collagenous colitis.