Colorectal cancer risk not increased overall in inflammatory bowel disease

[unseennude]

The risk of colorectal cancer in patients with inflammatory bowel disease (IBD) is similar to that of the general population, except for patients with extensive colitis, a Mayo Clinic study finds.

Researchers, led by Dr. William J. Sandborn, used data from the Rochester Epidemiology Project, collected from residents of Olmstead County, Minnesota, between 1940 and 2001.

They estimated the cumulative probability of cancer and standardized incidence ratios (SIRs) using expected rates from Surveillance, Epidemiology and End Results (SEER), data on white residents of Iowa between 1973-2000 and Olmstead County residents between 1980-1999. The results are published in the April issue of Gastroenterology.

Dr. Sandborn's team identified 692 Olmstead County residents diagnosed with IBD between 1940 and 2001. Colorectal cancer was diagnosed in six patients with ulcerative colitis. The expected number, according to estimates, was 5.38 (SIR, 1.1). Four of the six occurred among patients with extensive colitis and pancolitis (SIR, 2.4).

Six patients with Crohn's disease developed colorectal cancer, compared with the expected 3.2 (SIR, 1.9). Three patients with Crohn's developed small bowel cancer, compared with the expected 0.07 for the general population (SIR, 40.6).

As noted, the team found no increased risk of colorectal cancer among patients with ulcerative colitis except among those with extensive colitis. Dr. Sanborn and colleagues note that the risk was greater among Crohn's disease patients, particularly for those diagnosed before the age of 30.

Dr. David T. Rubin of the University of Chicago proposed some reasons for the lack of increased colorectal cancer in the IBD population.

"Therapy controls inflammation, and we believe that inflammation may be the cause of cancer," Dr. Rubin, the author of an accompanying editorial, told Reuters Health. "Some therapies have been proposed as chemopreventive for cancer, specifically the 5-aminosalicylic acid therapies. Surgery, when provided earlier, may remove a higher risk cohort and therefore lower the incidence of colorectal cancer."

"Although this information from Mayo is encouraging, it does not eliminate the need for patients to remain in surveillance and prevention programs," Dr. Rubin said