Risk and Management of Bowel Obstruction in Colorectal Cancer Patients Undergoing Immunotherapy: A Cross-Sectional Multicenter Study

Background: Despite the remarkable efficacy of immunotherapy for mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) colorectal cancer (CRC), patients may still develop bowel obstruction during tumor regression. Methods: The study cohort included CRC patients who received immunotherapy at four medical centers. Bowel obstruction risk was assessed, and clinicopathological and molecular features were recorded. A Bayesian model was used to identify risk factors. Results: A total of 214 patients were reviewed, with 196 patients meeting the eligibility criteria. Bowel obstruction occurred in 22 patients (10.3%) during immunotherapy. Obstruction was more commonly observed in patients with T4 stage tumors ( P = 0.008), metastatic disease ( P < 0.001), and an impassable lumen on baseline endoscopy ( P = 0.022). Multivariable analysis revealed that T4 tumor was identified as an independent risk factor (odds ratios: 8.36, 95% confidence interval: 1.20– 80.34). Among responders with obstructions, the median time to response was 6.1 weeks (interquartile range [IQR]: 5.5– 10.7), the best response was 9.9 weeks (IQR: 5.6– 23.6), and obstruction occurred at 6.6 weeks (IQR: 5.3– 9.2). Notably, 42.9% (6/14) of the patients developed obstructions after laxative use during endoscopy. Four patients (18.2%) required surgery. Three (21.4%) patients in supportive therapy experienced recurrent obstructions. Four patients underwent endoscopic treatment (two stents, two balloon dilatations), all with symptom relief. Conclusion: Bowel obstruction was common in CRC patients receiving immunotherapy. This risk may be suggested by two clinical features at baseline. Obstructions often occurred after the initial response but before the best overall response. Early detection and proper management may help to prevent or reduce obstructions. Keywords: colorectal cancer, immunotherapy, bowel obstruction, risk factors, management