Although inflammatory bowel disease (IBD) increases risk for colorectal cancer (CRC), the risk is only substantial among patients with long-term, extensive colitis. Furthermore, CRC risk is reduced by thiopurine therapy, according to the July issue of Gastroenterology.
Laurent Beaugerie et al. collected data from 19,486 patients with IBD (60% with Crohn’s disease, 40% with ulcerative colitis) and identified those that developed colorectal neoplasms within 10 years after diagnosis of IBD.
The authors found that overall, patients with IBD had a 2-fold greater risk of CRC than the general population. However, the subpopulation of patients with long-term, extensive colitis (the presence of >10 years of disease and >50% of colon affected by inflammation) had a 7-fold increase in risk for CRC, whereas patients without this extensive colitis had a similar risk to the general population.
The results were similar when the UC and CD populations were analyzed separately, so colon inflammation, rather than type of IBD, is what most affects cancer risk.
In an editorial that accompanies the article, Fernando S. Velayos and Thomas A. Ullman state that the finding that increase in CRC risk among patients with IBD comes primarily from the 15% with long-term, extensive colitis supports the current practice of screening this subgroup for cancer.
Beaugerie et al. also found that nearly 40% of the observed cases of high-grade dysplasia and CRC occurred within 10 years of IBD diagnosis—a point at which most surveillance guidelines recommend the initiation of screening and surveillance.
However, there are not sufficient resources to perform screening colonoscopies for all patients, every 1–2 years from IBD diagnosis. Velayos and Ullman say that studies are therefore needed to identify markers to separate these patients into low- and high-risk groups for CRC.
Beaugerie et al. reported that after adjustment for disease extent, duration and patients’ sex, thiopurine use reduced patients’ risk for CRC or high-grade dysplasia by 72%. However, Velayos and Ullman point out that the study did not address the effect of 5-aminosalicylate–based agents, so it is uncertain whether concurrent use of these agents confounded the observed effects of thiopurines.
It is not clear how thiopurines, which inhibit DNA and RNA synthesis and proliferation of lymphocytes, could have anti-neoplastic effects on colonic mucosa. Furthermore, these drugs have been reported to increase the risk for lymphoma, so Velayos and Ullman state that data do not justify use of thiopurines as chemopreventive agents.
Beaugerie et al. conclude that patients with long-term, extensive colitis are at increased risk of high-grade dysplasia and CRC, and that thiopurine therapy reduces this risk. However, patients without long-standing extensive colitis have a risk for CRC similar to that of general population, but they can develop neoplasias shortly after diagnosis of IBD.
Read the article online.
Beaugerie L, Svrcek M, Seksik P, et al. Risk of colorectal high-grade dysplasia and cancer in a prospective observational cohort of patients with inflammatory bowel disease. Gastroenterology 2013;145: 166–175.e8.
Read the accompanying editorial.
Velayos FS and Ullman TA. Looking forward to understanding and reducing colorectal cancer risk in inflammatory bowel disease. Gastroenterology 2013;145:47–49.