In average-risk people, screening colonoscopies were associated with a 70 percent reduction in risk for new, late-stage colon cancer, including hard-to-detect cancers on the right side of the colon. Advanced colon cancer is the least curable form.
Although colonoscopy is widely used as a screening test for colon cancer, there is little research that proves it is effective in reducing colon cancer deaths, according to the study authors. The researchers wanted to answer a simple question: If you ended up with late-stage cancer, were you more or less likely to have had a screening colonoscopy as many as 10 years before the disease was discovered?
The study authors also wanted to show whether a colonoscopy is able to evaluate the entire colon, including the right side, which is harder to adequately cleanse before the test, more difficult to reach, and often has pre-cancerous areas that are tougher to spot and identify.
"Colonoscopy has the ability to identify both left- and right-sided colon cancers before they have progressed to an advanced stage," said lead study author Dr. Chyke Doubeni, associate professor in the department of family medicine at the University of Pennsylvania.
The researchers also discovered that screening sigmoidoscopy, a less costly procedure that enables a physician to look at the part of the large intestine closest to the rectum, was linked to a significant reduction in late-stage disease in most of the large intestine, but not in the right colon.
However, the study does not show that colonoscopy or sigmoidoscopy is better than the much easier, far less expensive "fecal occult blood test" (FOBT), which is done at home by swiping a tiny amount of stool onto a card for three days, said Doubeni. "There is strong evidence showing the effectiveness of the [fecal occult blood test] when done annually. There is no reason, based on the knowledge we currently have, that you should switch to a colonoscopy if you're getting a FOBT every year," said Doubeni.
If simpler tests are effective, why are patients encouraged to undergo a colonoscopy? "Let me just say there are other factors beyond the evidence that are driving the use of colonoscopy in the U.S.," said Doubeni. "No other country uses colonoscopy for screening purposes as much as the United States, although Germany comes close," he noted.
The U.S. Preventive Services Task Force recommends that people 50 to 75 years old be screened for colon cancer in one of three ways: a home fecal occult blood test every year; a sigmoidoscopy every five years combined with a home fecal occult blood test every three years; or a colonoscopy every 10 years.
A colonoscopy examines the inside of the large intestine with a camera-tipped tube. The test enables the physician to remove any precancerous growths -- adenomatous polyps -- which sometimes develop into cancer. Colorectal tumors are a major cause of death from cancer in the United States, with about 137,000 new cases and 52,000 deaths every year, according to the U.S. Centers for Disease Control and Prevention.
For the study, published in the March 5 issue of the Annals of Internal Medicine, the authors reviewed health records of more than 1,000 average-risk adults between the ages of 55 and 85 who were members in four health management organizations (HMOs).
The researchers identified 474 people with late-stage colon cancer and then looked back 10 years to see if they had been screened for the disease with colonoscopy or sigmoidoscopy. They compared them to 538 "control" patients and used additional information from state or local tumor registries to see whether there was an association between having had a colonoscopy or sigmoidoscopy and developing cancer.
Dr. David Bernstein, a gastroenterologist at North Shore University Hospital in Manhasset, N.Y., said the study had a critical design flaw. "Making assumptions that any cancers that were found would have been seen 10 years prior doesn't make sense," he said. "It doesn't prove that these cancers didn't occur two years ago."
A key part of effective colon screening is getting the tests at the recommended interval, experts say. To better understand what might be effective in prodding people to get screening, another study published this month in the same journal found that people who were mailed a letter, a pamphlet and a fecal occult blood test kit completed recommended screening twice as often and for less cost than those who were not reminded or got automated and other reminders by nurse coaches.
Doubeni recommends something far more simple: doing the fecal occult blood test every year right around the time of your birthday.
