“…Histological clues to ICI colitis include: - crypt epithelial cell apoptosis 25 , 27 , 28 (variable definitions, including more than 3 apoptotic bodies within epithelium of 10 crypts, 23 more than one apoptotic cell per biopsy, 29 more than 5 apoptotic bodies per 100 crypts 9 ). Excess apoptosis can be seen without accompanying inflammation, producing a GVHD‐like pattern of injury, or in combination with acute colitis or chronic active colitis 17 (Figure 2a )
- atrophic crypts with attenuation of crypt epithelium, 17 , 18 , 30 sometimes with an intraluminal admixture of apoptotic debris and inflammatory cells 13 , 17 , 18 , 23
- intra‐epithelial lymphocytosis (more than 10 intraepithelial lymphocytes within 100 surface epithelial cells) 23 , 25 , 27 , 30 , 31
- a mild (rather than moderate/severe) degree of CAD 16 , 28 (Figure 2a – c ), less frequent basal plasmacytosis, 28 fewer lamina propria plasma cells, less subcryptal inflammation, lower overall chronicity scores compared to IBD 23
- Lesser degree of cryptitis and crypt abscesses compared to UC 28
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