Benefits of Colonoscopy Seen More Limited?

Cancer of the colon is one of the most common causes of death from cancer, coming in just behind lung cancer, among the many types of cancer that affect men and women. Most cancers of the colon begin as polyps which are small, slow-growing, mushroom-like growths on the inner surface of the colon. The purpose of colon cancer screening is to detect and remove growths before they invade and spread. 

 

A colonoscopy screening is performed to inspect the entire colon through a flexible tube. Because colonoscopy is also the most expensive, inconvenient, and riskiest test, it is important to know whether colonoscopy reduces the chance of dying of colon cancer. Researchers performed studies to find out whether the colon cancer death rate is lower in people who had a colonoscopy performed.

 

Previously believed that screening for colorectal cancer through a colonoscopy prevents up to 90 percent of deaths studies now indicate that the number is closer to only two-thirds. Further studies show that only those with malignancies that occur on the left side of the colon benefit from preventing death through colonoscopy procedures.

 

"While colonoscopy remains the gold standard for evaluation of the colon, our study sheds light on some of the real-world limitations of this practice for screening and prevention," lead author Dr. Nancy Baxter, from the University of Toronto, said in a statement.

The large bowel extends from the rectum up the left side of the abdomen, across, and down the right side to the cecum, or junction with the small intestine. Although the entire colon should be inspected during a colonoscopy, the cecum and the right side of the colon can be difficult to reach during insertion of the colonoscope.

The biggest limitation was the lack of information in the computer records about the purpose of the colonoscopy: to screen people who had no symptoms of colon cancer or to evaluate symptoms that could be caused by colon cancer. The other limitation is that people were not randomly assigned to get a colonoscopy. Therefore, it is not possible to say that a colonoscopy is a cause of a lower death rate from colon cancer.

The current study, based in Ontario, Canada, included more than 10,000 patients who were diagnosed with colorectal cancer between 1996 and 2001 and died from the malignancy by the end of 2003. Each patient was matched to five "controls" who did not have colorectal cancer.

Overall, 9.8 percent of controls had undergone a colonoscopy compared with only 7.0 percent of the patients who died of colorectal cancer, the researchers report in the Annals of Internal Medicine.

Complete colonoscopy (that is, to the cecum) was associated with a 67 percent reduced risk of death from left-sided colorectal cancer, but was not associated with a significant reduction in deaths from right-sided disease. One reason for this may be that the colonoscopies were not as complete as reported, or were hurried, Dr. David F. Ransohoff, from the University of North Carolina at Chapel Hill, suggests in an accompanying editorial.

He comments, "Colonoscopy is an effective intervention, but as Baxter and colleagues suggest, we must realize that current evidence is indirect and does not support a claim of 90 percent effectiveness." Ransohoff adds that, in advising patients about colonoscopy, "we should be realistic and cautious when talking with them about the magnitude of both benefits and risks."