IMMUNOTHERAPHY INDUCED COLITIS MIMICKING INFLAMMATORY BOWEL DISEASE: A SYSTEMATIC REVIEW AND META-ANALYSIS

Abstract INTRODUCTION The recent use of checkpoint inhibitors, including anti-PD-1/PD-L1/CTLA-4 antibodies, in treating various malignancies has certainly changed the therapeutic landscape. Still, it also comes with various adverse effects ranging from endocrinopathy to Colitis. CPI-induced colitis has become a growing challenge for clinicians to address in recent years due to its close resemblance to Inflammatory bowel disease (Crohn’s & ulcerative colitis). METHODS We did a systematic search of PubMed, EMBASE, and Cochrane Library through April 2025. Studies with reported CPI-induced colitis and its histological, morphological, and clinical comparison with IBDs were selected. Data selection was based on CPI type, endoscopic findings, timing of symptoms onset, involvement of the colon segment, histopathology, and treatment outcomes. A random effect model was used to conduct this meta-analysis. RESULTS Eighteen studies with 1,246 patients with CPI-induced colitis were selected. Ipilimumab (Anti-CTLA-4) was associated with severe colitis and pancolitis. Nivolumab & Pembrolizumab (Anti-PD-1) showed a localized disease pattern, while Atezolizumab (PD-L1) showed focal or patchy colitis with mild to moderate severity. Endoscopic findings with continuous inflammation in the rectosigmoid resembling UC were demonstrated in 43% of the cases. 38% of the cases showed crypt architectural distortion. Left colonic segmental involvement was seen in 63.8% of the cases compared to the right colonic segment, which was seen in 22% of the cases. Pooled odds ratio for CPI colitis mimicking UC vs Non-specific colitis was 2.91 (95% CI: 2.01-4.22). Heterogeneity was moderate (I2=58%). Per the NCCN guidelines, Steroids, Infliximab, and Vedolizumab were effective treatment options. The results are presented in the tables and figures below. CONCLUSION Colitis induced by CPI often mimics UC both endoscopically and histologically and involves the rectosigmoid specifically. Ipilimumab which is an anti-CTLA-4 agent, is frequently associated with a UC like colitis, which is characterized by diffuse, continuous mucosal inflammation and crypt architectural distortion. In contrast, PD-1 inhibitors, including nivolumab and pembrolizumab, tend to cause segmental, patchy inflammation and sometimes resembles Crohn’s disease, though histologic features are less specific. Due to the diverse pattern of disease, it is very crucial to recognize CPI induced colitis in order to initiate appropriate therapy and achieve optimal outcomes.