Inflammatory bowel disease and risk of adenocarcinoma and neuroendocrine tumors in the small bowel

Background: Uncertainty prevails about the magnitude of excess risk of small bowel cancer in patients with inflammatory bowel disease (IBD). Patients and methods: To quantify the risk of small bowel adenocarcinoma and neuroendocrine tumors in patients with ulcerative colitis (UC) and Crohn's disease (CD), we undertook a population-based cohort study of all patients with IBD diagnosed in Norway and Sweden from 1987 to 2016. Patients were followed through linkage to national registers. We calculated standardized incidence ratios (SIRs) with 95% confidence intervals (Cis) of small bowel adenocarcinomas and neuroendocrine tumors for patients with CD and UC. We excluded the first year of follow-up to reduce reverse causality. Results: Among 142 008 patients with a median follow-up of 10.0 years, we identified 66 adenocarcinomas and 57 neuroendocrine tumors in the small bowel. The SIR of small bowel adenocarcinoma was 8.3 (95% CI 5.9-11.3) in CD and 2.0 (95% CI 1.2-3.1) in UC. The incidence rates of adenocarcinomas were highest in CD with stricturing disease and extent limited to the small bowel, at 14.7 (95% CI 8.2-24.2) and 1S.8 (95% CI 8.4-27.0) per 100 000 personyears, respectively. The SIR of neuroendocrine tumors was 2.5 (95% CI 1.5-3.9) in CD and 2.0 (95% CI 1.4-2.8) in UC. Conclusions: Patients with CD experienced an eightfold increased risk of small bowel adenocarcinomas, patients with both UC and CD experienced an about twofold increased risk of neuroendocrine tumors, and patients with UC experienced a twofold increased risk of small bowel adenocarcinoma. The small absolute excess cancer risk suggests that active surveillance to diagnose small intestinal cancer early is unlikely to be cost-effective.