Among the microscopic-like phenotypes, an increased presence of intra-epithelial lymphocytes, mimicking lymphocytic colitis, is reported in a minority of cases (10–12%), especially in patients treated with anti-CTLA-4 antibodies [138,147]; conversely, a collagenous colitis-like phenotype is rarer and associated with anti-PD-1 anti-PD-L1 [139,148]. Here, CTLA4 is linked to collagenous colitis.