New findings by California researchers may change the way doctors think about colonoscopy -- a popular screening test for colon and rectal cancer.
The research suggests that flat lesions growing on the colon wall are more common than previously thought -- and are five times more likely to be cancerous than the more well-known, protruding growths called polyps. Many doctors are not as familiar with the flat lesions, which are much more difficult to spot during colonoscopy, and may not know how dangerous they can be.
"It has been thought in the past that big polyps were the big players that turned into cancer," said Dr. Peter Darwin, director of gastrointestinal endoscopy at the University of Maryland Medical Center. This and future studies "may change the way we think about cancer."
The research offers possible solutions to one mystery: why colon cancer, in some rare cases, appears not long after colonoscopy -- even when doctors found no abnormalities.
Standard practice has assumed that when no polyps are found during a colonoscopy, the patient is free of cancer and doesn't need to be rescreened for a decade -- the amount of time it is believed to take for a polyp to grow and become cancerous. But if pre-cancerous growths -- such as flat lesions -- are missed or not completely removed, cancer can develop between screenings.
Darwin noted that colon cancer is one of the few cancers that can be prevented, by removing polyps found during colonoscopy. Though the vast majority of cancers begin as polyps, some might start as these subtle, flat or even depressed lesions.
The study, published this month in the Journal of the American Medical Association, underscores the need to have a colonoscopy performed by well-trained and experienced physicians, doctors said.
"It's been shown very clearly that colonoscopy, even in the best hands, is going to miss 5 to 10 percent of abnormalities," said Dr. Durado Brooks, director of colon cancer for the American Cancer Society. "It's [the public's] perception that colonoscopy is almost a 100 percent accurate tool, and that's simply not the case. It's a very good tool, but it is not a perfect tool.
"Letting the perfect be the enemy of the good is a mistake. Colonoscopy is the best tool we have."
