Flat colorectal tumors relatively common in US population, linked to cancer

March 4, 2008

NEW YORK (Reuters Health) - Although the focus of colorectal cancer prevention efforts in Western populations is usually on the detection and removal of polypoid neoplasms, findings from a US study indicate that even in this country, flat tumors are fairly common and are more strongly linked to cancer than are polypoid tumors.

According to the report in the March 5th issue of Journal of the American Medical Association, about 1 in 11 patients who undergo elective colonoscopy will be found to have a non-polypoid tumor. Almost 1% of these tumors harbor in situ or invasive carcinoma, which is roughly 10 times the rate seen with polypoid tumors.

"A number of prior studies suggested that flat lesions were not commonly found in North American patient population and the rates of high-grade dysplasia in small flat polyps were low," lead author Dr. Roy M. Soetikno told Reuters Health. "Thus, there was a significant skepticism of the importance of the non-polypoid neoplasm."

This skepticism, according to Dr. Soetikno, with the VA Palo Alto Health Care System in California, may stem from clinicians mistakenly equating "flat" with "small". However, he noted, the current findings show that irrespective of lesion size, non-polypoid lesions are more likely to harbor cancer than polypoid ones.

The study involved 1819 patients from the researchers' center who underwent colonoscopy performed by one of four endoscopists, all of whom were proficient in the detection of non-polypoid lesions.

Overall, 9.35% of patients had non-polypoid lesions, the authors report. In a surveillance subpopulation, the prevalence reached 15.44%.

"The overall prevalence of non-polypoid colorectal neoplasms with in situ or submucosal invasive carcinoma was 0.80%," the investigators found. In the subpopulation of patients undergoing cancer screening, the prevalence was 0.32%.

Non-polypoid lesions were 9.78-times more likely to contain cancer than were polypoid ones, the report shows, and, as noted, this was irrespective of tumor size. In the surveillance subpopulation, the odds ratio climbed to 63.7.

Dr. David Lieberman, author of a related editorial and a gastroenterologist with the Oregon Health & Science University in Portland, comments that "these findings may have implications for colorectal cancer screening."

The finding that "non-polypoid colorectal neoplasms have high rates of serious pathology suggests that effective screening programs will need to accurately identify patients who harbor these lesions."