March 6, 2008 -- They are usually missed or overlooked during colon cancer screening, but flat lesions within the lining of the colon and rectum may be more likely to be cancerous than polyps, new research shows.
They are also more common in the U.S. population than previously thought.
Known as nonpolypoid colorectal neoplasms, they were found in roughly 9% of patients who underwent colonoscopy in the new study, published in today's edition of The Journal of the American Medical Association.
And the flat lesions were roughly five times more likely to contain cancerous tissue than polyps, after adjusting for polyp size.
"This study shows that flat lesions are actually a lot more dangerous than protruding ones," researcher Roy M. Soetikno, MD, tells WebMD. "We can do a better job of preventing colon cancer if we look for them, but this will require that the patient and the doctor work together."
Spotting Flat Lesions
The flat or even recessed lesions are much more difficult to spot than raised polyps with traditional colonoscopy, because their appearance is similar to normal tissue.
Soetikno says patients can help by doing everything their doctor recommends to prepare for a colonoscopy. The lesions are even harder to spot if any waste is left in the bowel.
And doctors must be made aware of the importance of the nonpolyp lesions, and do a thorough job of looking for them.
In the study, Soetikno and colleagues using a special dye to highlight subtle changes seen with standard high-resolution colonoscopy.
This takes much longer than a standard colonoscopy, but it is an important step, Soetikno says.
New-generation endoscopes don't require the dye step, and they may be able to detect the lesions more accurately and quickly than older endoscopes.
Studies suggest that about one in four colonoscopies are compromised by poor bowel cleanout.
"You can't overstate the importance of the prep for a good-quality exam," American Society for Gastrointestinal Endoscopy President Grace Elta, MD, tells WebMD. "You hear over and over that the prep is the worst part, but it is also the most important part."
Depressed Lesions Most Dangerous
The study involved 1,819 veterans who underwent elective colonoscopy in Palo Alto, Calif.
A total of 9.35% of patients had the flat or depressed lesions.
The depressed type of lesion, which was the most difficult to detect during colonoscopy, had the highest likelihood of containing precancerous or cancerous tissue.
The incidence of the lesions was found to be similar to that reported in Japanese populations, a group that researchers had believed were uniquely susceptible to them.
And the size of the lesions did not appear to be a factor in whether or not they contained cancer cells.
Colonoscopy Still Highly Effective
The lesions were also most commonly seen in people who also had large polyps or symptoms suggestive of colon cancer.
American Cancer Society Director of Screening Robert Smith, PhD, tells WebMD that this is reassuring.
"The likelihood that a person with a normal colonoscopy is harboring a really dangerous abnormality is not very high," he says.
The experts who spoke to WebMD all agreed that standard colonoscopy remains a highly effective tool for screening and preventing colon cancer and that people who have had one do not need another one to look for flat lesions.
"I don't think people should be overly concerned that they may have had a poor procedure," American College of Gastrointerology President Amy Foxx-Orenstein, DO, says. "The most important thing is to be screened and to follow up that screening as recommended."