If you asked a group of doctors what they were looking for when they performed a colonoscopy, most would probably describe a typical polyp -- a protruding pink growth that looks like a cauliflower on a stalk. But a study published in the Journal of the American Medical Association suggests that doctors need to have something else in mind as well: a lesion that is flat or even slightly depressed.

Japanese doctors began publishing reports about these flat, or nonpolypoid, lesions in the 1980s, describing them as both hard to find during colonoscopy and more likely to be cancerous than typical polyps. At that time, there was little evidence that these lesions were as common in the United States as they were in Japan, so these reports drew little attention.

But in 1999, a research group at a Veterans Affairs (VA) hospital in Northern California became interested in the lesions. And they decided to investigate whether they were uncommon in the United States or just not being found.

Before they began their study, the VA research group trained with Japanese doctors who had extensive experience finding and removing flat lesions during a colonoscopy. Once the VA doctors felt comfortable with their ability to detect flat lesions, they began their research study, tracking the types of lesions they found during colonoscopy procedures.

Over the next year, they performed colonoscopy procedures on 1,819 veterans, mostly men. The doctors found that 170, about 9%, of the patients had a flat lesion, and 15 of these flat lesions were early-stage or invasive cancer.

Further analysis revealed that the flat lesions were more than five times as likely to be cancerous as similarly sized regular polyps. Moreover, the polyps that were slightly depressed, though less common than the other flat lesions, had the highest likelihood of being serious.

This study suggests that the rate of flat lesions in the United States is similar to that in Japan. However, because most of the people in this study were white men, more research is needed to see if flat lesions develop at the same rate in women and other ethnic groups.

Also unknown is whether more frequent follow-up colonoscopy procedures may be advisable when flat lesions are identified and whether removal of these polyps actually cures or prevents colon cancer -- as has been shown with early removal of regular polyps.

Long-term studies are needed to answer all of these questions. Even so, the VA study underscores the need for U.S. doctors who perform colonoscopies to receive training on how to identify and remove these flat lesions.

What This Means for You. If you recently had a colonoscopy, this new information about lesions doesn't mean you need to schedule another one right away. However, there are a number of things you can do to ensure that you continue to get proper colonoscopy screening. Be sure to:

• Talk to the doctor who performs your colonoscopy. Ideally, he or she should have received the training necessary to find flat lesions. If this type of expertise is not available in your area, be sure the doctor routinely spends at least six to 10 minutes examining the colon as the endoscope is withdrawn. Recent research shows that slower withdrawal times improve detection.
• Follow all colonoscopy preparation instructions. Flat lesions are impossible to see if the colon is not completely cleansed before the procedure.
• Follow your physician's advice if you're told to return for a repeat colonoscopy. Studies show that people often do not follow their doctor's recommendation to have a repeat exam.
• Pay attention to possible colorectal cancer symptoms. If you experience problems that might be symptoms of colorectal cancer, such as rectal bleeding or a change in your bowel habits, tell your doctor right away and return for a repeat colonoscopy as soon as possible.