PDCD1 and lymphocytic colitis: Whereas, anti-PD-1-related colitis typically follows one of two patterns: active colitis with apoptosis (active inflammation, neutrophilic crypt micro-abscesses, increased crypt epithelial cell apoptosis) or lymphocytic colitis (increased intraepithelial lymphocytes in surface epithelium and expansion of the lamina propria (4).