There is an unclear risk of colonic high-grade dysplasia (HGD) and colorectal cancer (CRC) among patients with inflammatory bowel disease (IBD) treated with immunosuppressants. We analyzed data on CRC development among patients with IBD enrolled in the observational cohort Cancers et Surrisque Associé aux Maladies Inflammatoires Intestinales En France (CESAME).

We followed and collected data from 19,486 patients with IBD (60.3% with Crohn's disease, 30.1% receiving thiopurine therapy) enrolled in CESAME from May 2004 and June 2005, and followed them until December 2007. When the study began, 2841 patients (14.6%) were characterized as having long-standing extensive colitis (ie, >10 years and involving ≥50% of the colon). Early lesions (HGD and CRC) were defined as those diagnosed within 10 years after diagnosis of IBD.

Thirty-seven patients developed CRC during the follow-up period, and 20 developed colorectal HGD. The standardized incidence ratios of CRC were 2.2 for all IBD patients (95% confidence interval [CI]: 1.5−3.0; P < .0001), 7.0 for patients with long-standing extensive colitis (95% CI: 4.4−10.5; P < .001), and 1.1 for patients without long-standing extensive colitis (95% CI: 0.6−1.8; P = .84). Among patients with long-standing extensive colitis, the multivariate adjusted hazard ratio for colorectal HGD and cancer was 0.28 for those who received thiopurines compared with those who never received thiopurine therapy (95% CI: 0.1−0.9; P = .03). Twenty-two patients developed early lesions; 7 of these were related to IBD, based on histologic analysis.

Patients with IBD and long-standing extensive colitis are at increased risk for CRC, although the risk is lower among patients receiving thiopurine therapy. Patients without long-standing extensive colitis have a risk for CRC similar to that of the general population, but they can develop IBD-related lesions within 10 years after diagnosis of IBD.