The risk for colorectal cancer (CRC) in patients with inflammatory bowel disease (IBD) could have changed over time, with changes in treatment options. We studied CRC risk in a nationwide cohort of 47,374 Danish patients with IBD over a 30-year period.

We determined relative risk (RR) values using Poisson regression-derived incidence rate ratios of CRC from 1 year after IBD diagnosis, adjusted for age, sex, and calendar time. We compared incidence of CRC among patients with IBD vs individuals without IBD.

During 178 million person-years of follow-up evaluation, 268 patients with ulcerative colitis (UC) and 70 patients with Crohn's disease (CD) developed CRC. The overall risk of CRC among patients with UC was comparable with that of the general population (RR, 1.07; 95% confidence interval [CI], 0.95–1.21). However, patients diagnosed with UC in childhood or as adolescents, those with long duration of disease, and those with concomitant primary sclerosing cholangitis were at increased risk. For patients with UC, the overall RR for CRC decreased from 1.34 (95% CI, 1.13–1.58) in 1979–1988 to 0.57 (95% CI, 0.41–0.80) in 1999–2008. Among patients with CD, the overall RR for CRC was 0.85 (95% CI, 0.67–1.07), which did not change over time.

A diagnosis of UC or CD no longer seems to increase patients' risk of CRC, although subgroups of patients with UC remain at increased risk. The decreasing risk for CRC from 1979 to 2008 might result from improved therapies for patients with IBD.