A colonoscopy is performed by a doctor who inserts a long, flexible tube with a camera on the tip into the rectum to scan the colon for polyps or cancer. The procedure is recommended for people over age 50. Doctors also recommend it more frequently for people with a strong family history of cancer or those who have had polyps found in prior colonoscopies.
If the test comes back normal, doctors typically say the patient need not get a repeat colonoscopy for a decade. But if symptoms such as a change in bowel habits or blood in the stool appear within a few years of a colonoscopy, it could be a sign that something was missed -- and Brooks said a patient may need another procedure.
The JAMA study is among the first to find evidence of flat lesions in Americans. But studies in Japan dating to the 1980s suggest that these lesions were "common and ominous," Dr. David Lieberman, a gastroenterologist at the Oregon Health & Science University in Portland, wrote in an editorial accompanying the study.
Similar studies in the U.S. did not find the same evidence until this one, involving 1,819 patients at the Veterans Affairs Palo Alto Health Care System, where about 10 percent had these flat lesions.
Some doctors said further studies are needed to see if the lesions found among the mostly white, mostly male population in California can be extrapolated to other groups.
The doctors who treated the patients in the study received training in colonoscopy procedures used in Japan, where flat lesions are better understood. They used equipment that sprayed a blue dye on suspicious patches and made them easier to decipher.
The study also emphasized the need for the bowel to be fully emptied before the procedure is done, so that flat lesions aren't obscured.
The day after the study appeared, the American Cancer Society and other health groups endorsed two new screening tests for colorectal cancer. One is the virtual colonoscopy, which uses a CT scan to search for growths.
It is unclear whether the latest findings will have any impact on those guidelines in the future, since the virtual test is "not going to be able to detect a flat adenoma," said Dr. Michael Choti, director of the Johns Hopkins Colon Cancer Center.
Nationwide, the proportion of people older than 50 who had a colonoscopy or a similar procedure over the previous 10 years rose from 45 percent in 2002 to 56 percent in 2006, according to a recent Centers for Disease Control and Prevention survey.
