Published: March 5, 2008
An easily overlooked type of abnormality in the colon is the most likely type to turn cancerous, and is more common in this country than previously thought, researchers are reporting.
»
Prevalence of Nonpolypoid (Flat and Depressed) Colorectal Neoplasms in Asymptomatic and Symptomatic Adults (JAMA)
The findings come from a study of colonoscopy, in which a camera-tipped tube is used to examine the lining of the intestine. Generally, doctors search for polyps, abnormal growths that stick out from the lining and can turn into cancer. But another type of growth is much more dangerous, and harder to see because it is flat or depressed and similar in color to healthy tissue.
Japanese researchers became concerned about these flat lesions in the 1980s and ’90s, but studies here had mixed results and American doctors tended to think that flat growths were less common and less dangerous in the United States.
The new study, to be published Wednesday in the Journal of the American Medical Association, suggests otherwise.
Some doctors in this country were already alert to flat lesions, but the findings will pose a challenge to others, because it takes a trained and vigilant eye to see the growths and special techniques to remove them. The results also mean it is especially important that patients take the harsh laxatives that many dread in advance of the test. The flat lesions, hard to find even under the best conditions, will be impossible to see if any waste is left in the bowel.
Colon cancer is the second-leading cause of cancer death in the United States, after lung cancer, with about 154,000 new cases detected and 52,000 deaths a year. It is one of the few cancers that is totally preventable if precancerous growths are found and removed; it can also be cured with surgery alone if found early enough.
People who have just had a colonoscopy should not rush to schedule another one just to look for the flat growths, doctors said.
“I don’t think people have to panic that they’ve somehow been neglected and had poor care,” said Dr. David A. Rothenberger, deputy chairman of surgery at the University of Minnesota.
But he and other experts emphasized that people should see a doctor any time they have persisting symptoms that could indicate colon cancer, like rectal bleeding or a change in bowel habits — no matter how recently they had a colonoscopy. The test is highly reliable, but not perfect, doctors say.
Some doctors who perform colonoscopy just are not good at seeing flat lesions, but may improve with training and practice, said Dr. Douglas K. Rex, a gastroenterologist and professor of medicine at Indiana University.
“I think there are people who expect everything in there to be shaped like a golf ball,” he said. “It’s not.”
Dr. David Lieberman, chief of gastroenterology at Oregon Health and Science University, who wrote an editorial accompanying the study, said: “I think there will be some surprise. There has been in general some skepticism in the United States about how common flat and depressed lesions are and how important they are. So I think this study, coming from the United States and from a good group of investigators, will be a wake-up call to a lot of physicians and will prompt people to be looking for these lesions.”
The study, of 1,819 military veterans, mostly men, found that 9.35 percent had flat lesions, and those lesions were five times as likely as polyps to contain cancerous or precancerous tissue. Depressed or indented lesions were the least common but the most risky. Together, the flat or depressed lesions accounted for only 15 percent of the potentially cancerous growths found in the study, but were involved in half of the cancers. Once the doctors spotted the flat lesions, they sprayed a bluish dye on them to see their outlines better and remove them completely.
The first author of the study, Dr. Roy M. Soetikno of the Veterans Affairs Palo Alto Health Care System said, “The message for doctors is, Here is a large amount of data showing that these precursors of cancer, always believed to be a Japanese disease, are actually a disease here, and are important, because they are much more likely to be cancerous, and doctors need to spend the time to provide quality colonoscopy.”
The message to patients, Dr. Soetikno said, is that when preparing for colonoscopy, they must follow instructions to the letter and take the hated laxatives to make sure their bowels are empty so that doctors can see the lining.
If any waste remains, flat lesions will be buried by it. Studies have shown that in about a quarter of all colonoscopies, the bowel preparation is inadequate.
Dr. Rex said that male veterans tended to have more precancerous colon growths than other groups, so the rate of flat lesions in women or the general population might not be quite as high as those in the study.
Dr. Soetikno and his colleagues started an exchange program with doctors in Japan to learn their techniques for recognizing and removing the flat lesions.
American doctors should learn from overseas colleagues more often, Dr. Rothenberger said, adding, “We tend to get very smug about our abilities.”
The quality of colonoscopy has become a delicate issue, because an article in The New England Journal of Medicine in December 2006 found that some doctors were 10 times better than others at finding precancerous polyps. A major factor in their success was taking enough time to examine the colon thoroughly, as opposed to rushing through the procedure. Doctors who miss polyps would almost certainly miss flat lesions as well because they are harder to see. The new study underscores the need for careful examinations, because the flat lesions are more dangerous.
The study also raises doubts about whether “virtual colonoscopy,” performed by a CT scanner, will ever be able to take the place of the colonoscope inserted into the rectum, as many patients had hoped. The problem is that CT scans use X-rays to reveal shapes, and find polyps because they stick out. Flat lesions are unlikely to show up in such scans.
Studies show that from 0.3 percent to 0.9 percent of patients develop colon cancers within just a few years of having a colonoscopy and polyp removal — exactly what the procedure is supposed to prevent. Some doctors think that flat lesions, missed entirely during the colonoscopy or not fully removed, may account for some of these apparent failures.
Dr. Robert Smith, the director of screening for the American Cancer Society, said flat lesions were “a vexing issue” that had provoked a lot of arguments among doctors.
“This paper shows they’re more prevalent than we believed, and also quite serious with regard to the presence of features associated with an elevated risk of cancer,” Dr. Smith said.
The difficulty facing patients is how to be sure their doctors are doing a good job. Professional groups have issued guidelines about the best way to perform a colonoscopy, but they are recommendations, not rules. The groups also urge doctors to track their own success rates at finding precancerous growths to see how they measure up to standards, but even if they do keep track, the doctors do not have to share the data with anyone. And many people are loath to ask about it. The doctor wielding the scope is the last person most patients would want to offend.
“The patient really has no way to act as an informed consumer,” Dr. Smith said. “You can’t call up a facility and say, ‘By the way, is my doctor any good?’ or, ‘Tell me who the best one is.’ ”
He added: “For some physicians there is an expectation of trust, and it is offputting to have a patient request documentation of competence. However, some physicians know patients are hearing about these issues and are not offended by questions about performance and errors.”
