Insights into colorectal cancer screening

Oct 2 2007

Two studies in the October issue of the journal Gastroenterology may help in refining recommendations for the use of colonoscopy to screen for colorectal cancer.

One study reports that patients with large polyps or adenomas—pre-cancerous growths that may develop into colorectal cancers—on initial colonoscopy may need more frequent follow-up, while those with only a few small polyps can be screened less often. The second study suggests that relatives of patients with large polyps should also be targeted for screening.

Dr. David A. Lieberman and colleagues of the Department of Veterans Affairs (VA) Medical Centers in Portland, Ore., compared the results of follow-up colonoscopy in two groups of patients. One group of 895 patients had some type of colorectal neoplasia—polyps or cancers—detected on their initial colonoscopy. The other 298 patients had no polyps or cancers.

When colonoscopy was repeated five years later, advanced polyps or cancers were found in approximately seven percent of the patients with previous polyps, compared to two percent of those without previous polyps.

The "more severe" the abnormalities at initial colonoscopy, the greater the likelihood of detecting large polyps (ten millimeters or larger) or cancers at follow-up. The risk was five times higher for patients with three or more small polyps and six to seven times higher for those who had large polyps or polyps with certain pre-cancerous changes (villous adenoma or high-grade dysplasia). For patients with one or two small polyps, there was no significant increase in risk.

The second study, led by Vanessa Cottet, M.Sc., of Université de Bourgogne, France, asked whether family members of patients with large polyps were more likely to have abnormal results on colonoscopy. Large polyps or colorectal cancers were found in about eight percent of 168 first-degree relatives—parents, children, or siblings—of patients with large polyps. This was twice as high as the rate of abnormalities in a group of 307 patients undergoing colonoscopy for other reasons.

For the family members, risk was even higher when the original patient was male, less than 60 years old, or had polyps located deeper (more distal) in the colon. "[T]here is now evidence to suggest that first-degree relatives of patients with large adenomas may need to be screened and monitored as carefully as relatives of patients with colorectal cancer," the authors suggest. In contrast, the likelihood of finding smaller polyps was no higher for relatives versus comparison patients.

The studies may help efforts to refine the recommendations for screening colonoscopy. "If we know more about risk factors for advanced neoplasia and could electively stratify risk, then screening could be tailored—that is, targeted to persons with high risk and away from those with low risk, who could either be examined with less invasive methods or perhaps not at all," writes Dr. Thomas F. Imperiale of Indiana University in an accompanying editorial.

Of more than 14 million colonoscopies performed in 2002 in the United States, about 40 percent were for screening while more than 20 percent were for follow-up of patients with previous suspicious polyps or colorectal cancer. Although colonoscopy is a powerful tool for screening, diagnosis, and management, it is a limited resource, according to Dr. Imperiale's editorial. If colonoscopy is not properly allocated, some patients may receive no colorectal cancer screening at all.

The results of the VA study support current recommendations for follow-up colonoscopy in patients with large polyps and other advanced neoplasia. Depending on the size, type, and number of polyps, screening may need to be performed every three years—compared to every year for patients with colorectal cancer and every five to ten years for those with no abnormalities. In contrast, patients with only one or two small polyps may be treated nearly the same as those with no polyps.

The results of the family study may help in deciding when to screen patients with a family history of large polyps. The researchers emphasize the need for further studies to determine the best approach to screening in relatives of patients with colorectal neoplasia, including possible alternatives to colonoscopy.