Objectives: It has been suggested that inflammatory bowel disease (IBD) and colon cancer are associated because they have genetic susceptibility in common, rather than IBD causing cancer. We examined the risk of colorectal cancer in first-degree relatives of patients with IBD in order to evaluate if they share the same genetic susceptibility.
Methods: We identified patients with IBD in the Danish Hospital Discharge Registry. A cohort of all first-degree relatives to these patients were linked to the Danish Cancer Registry. Colorectal cancers observed were compared with expected values based on age, gender, and calendar-specific incidence rates in the general population.
Results: Among 4,496 patients with IBD, a total of 19,645 relatives were identified. For parents of patients with Crohn's disease, we observed 19 cases of colorectal cancer compared with 20 expected (standardized incidence ratio [SIR] = 1.0, 95 percent confidence interval [CI] = 0.6-1.5). For parents of patients with ulcerative colitis, 55 cases were observed compared with 51 expected (SIR = 1.1, CI = 0.8-1.4).
Conclusions: The study did not corroborate the hypothesis that the same genetic factors play a significant role in the etiology of colorectal cancer and IBD, but more information is needed to disregard the possible link between IBD and colon cancer.