Occurrence of Colorectal Cancer and the Influence of Medical Treatment in Patients With Inflammatory Bowel Disease: A Danish Nationwide Cohort Study, 1997 to 2015

Background: The risk of colorectal cancer (CRC) for patients with inflammatory bowel disease (IBD) has previously been investigated with conflicting results. We aimed to investigate the incidence and risk of CRC in IBD, focusing on its modification by treatment. Methods: All patients with incident IBD (n = 35,908) recorded in the Danish National Patient Register between 1997 and 2015 (ulcerative colitis: n = 24,102; Crohn's disease: n = 9739; IBD unclassified: n = 2067) were matched to approximately 50 reference individuals (n = 1,688,877). CRC occurring after the index date was captured from the Danish Cancer Registry. Exposure to medical treatment was divided into categories including none, systemic 5-aminosalicylates, immunomodulators, and biologic treatment. The association between IBD and subsequent CRC was investigated by Cox regression and Kaplan-Meier estimates. Results: Of the IBD patients, 330 were diagnosed with CRC, resulting in a hazard ratio (HR) of 1.15 (95% confidence interval [CI], 1.03-1.28) as compared with the reference individuals. However, when excluding patients diagnosed with CRC within 6 months of their IBD diagnosis, the HR decreased to 0.80 (95% CI, 0.71-0.92). Patients with ulcerative colitis receiving any medical treatment were at significantly higher risk of developing CRC than patients with ulcerative colitis who were not given medical treatment (HR, 1.35; 95% CI, 1.01-1.81), whereas a similar effect of medical treatment was not observed in patients with Crohn's disease or IBD unclassified. Conclusions: Medical treatment does not appear to affect the risk of CRC in patients with IBD. The overall risk of developing CRC is significantly increased in patients with IBD as compared with the general population. However, when excluding patients diagnosed with CRC within 6 months of their IBD diagnosis, the elevated risk disappears.