Histopathological Characteristics and Distinction of Immune Checkpoint Inhibitor-Related Colitis

Abstract Introduction/Objective Immune checkpoint inhibitors (ICPIs) represent a groundbreaking class of cancer immunotherapy for patients with various advanced-stage solid cancers. ICPIs have been associated with immune- related adverse events, with ICPI-related colitis being a prominent concern due to its potential for life-threatening clinical complications. Recognizing the histopathologic characteristics specific to ICPI-related colitis is crucial for pathologists to provide an accurate diagnosis. Here we have collected and analyzed colon biopsies from patients with ICPI-related colitis following treatment of ICPIs to identify its distinctive histopathologic features and differentiate it from other colitis. Methods/Case Report Colon biopsies are collected from patients with ICPI-related colitis after receiving CTLA-4 and PD-L1 inhibitors as treatment for advanced melanoma. Histopathological features, including epithelial mucin depletion, enterocyte apoptosis, basal lymphoplasmacytosis, cryptitis, glandular architectural distortion, and granuloma, are compared with those in other colitis including ulcerative colitis, Crohn’s disease, microscopic colitis, ischemic and infectious colitis. Immunohistochemistry is employed to analyze inflammatory cell populations and specific enterocyte subtypes. Results (if a Case Study enter NA) ICPI-related colitis, following treatment with Ipilimumab and Nivolumab, commonly presents as active colitis, either with or without chronic colitis. Less frequently, it manifests as microscopic colitis, infectious or ischemic colitis. The acute active form of ICPI-related colitis resembles acute colitis in infectious or ischemic colitis; however, prominent enterocyte apoptosis and intraluminal apoptotic debris are relatively unique features to ICPI-related colitis. The chronic active form of ICPI-related colitis resembles inflammatory bowel diseases, particularly Crohn’s disease, but ICPI-related colitis exhibits an inflammatory injury more affecting surface mucosa and less basal lymphoplasmacytosis. Notably, the most distinctive feature of ICPI-related colitis is the depletion of specific mucinous epithelium observed in our cohort. Conclusion Recognizing specific histopathologic features of ICPI-related colitis, such as mucinous epithelial depletion, enterocyte apoptosis, and surface-dominant inflammation, are essential for pathologists in accurately diagnosing and distinguishing this disease to ensure proper clinical management for patients receiving ICPI treatment.