Inflammatory Bowel Disease and Small Bowel Cancer Risk, Clinical Characteristics, and Histopathology: A Population-Based Study

Inflammatory bowel disease (IBD) may increase risk of small bowel cancer (SBC). However, little is known of the characteristics and features of IBD-SBC, due to a low number of cases worldwide. We performed a population-based study of IBD and SBC to calculate risk and increase our understanding of clinical characteristics and histopathological and molecular features. The study population consisted of all individuals aged 16 years or older living in Denmark during 1978–2010. Through linkage between national registers and subsequent scrutiny of medical records and pathology descriptions, we identified 40 cases of IBD-SBC. Risk was calculated by standardized incidence ratio (SIR) (observed/expected); patient characteristics were derived from medical files, and surgery specimens were obtained from hospitals nationwide for histopathological and molecular analyses. During 241,620 person-years of follow-up, 23 patients with Crohn’s disease developed small bowel adenocarcinoma (SIR, 14.38; 95% confidence interval, 8.78–22.20) and 9 developed neuroendocrine tumors (SIR, 6.83; 95% confidence interval, 3.13–12.97). No significantly increased risk of SBC was found among patients with ulcerative colitis. Most patients with SBC had moderate-to-severe Crohn’s disease with small bowel and upper gastrointestinal involvement. Assessment of surgical specimens of small bowel adenocarcinomas revealed a clear transition from inflammation to dysplasia and cancer, whereas no tumors had evidence of microsatellite instability. In a population-based study of patients in Denmark with IBD and SBC, we found risk of adenocarcinomas and neuroendocrine tumors to be increased among persons with Crohn’s disease. Most patients with IBD-SBC had extensive IBD of moderate-to-severe activity. Adenocarcinomas appeared to develop via an inflammation-dysplasia-carcinoma pathway, but differed from IBD-related colorectal adenocarcinomas in their molecular features.