Screening for cancer is the best way to prevent many forms of the disease, particularly in skin and breast tissue, among other cancers, but the tests aren’t always the easiest to endure.
Take colonoscopy, the highly touted yet fidget-inducing method for detecting growths in the intestines. Despite the discomfort of having a scope threaded through the rectum to explore the entire colon, a colonoscopy has the benefit of being a screening tool and treatment procedure in one. Not only does the test find potentially cancerous growths, but a surgical attachment fixed to the end of the scope can remove them as well. (More on Time.com: Even Small Amounts of Holiday Drinking Boost Cancer Risk)
Yet despite the fact that nearly every health organization recommends that people over age 50 screen for colon cancer, recent studies have questioned how effective colonoscopy is in detecting pre-cancerous lesions, especially when compared to less expensive, and less invasive options such as testing fecal material, using a flexible sigmoidoscope, or even a virtual colonoscopy, in which technicians image the colon without physically entering it with a tiny camera. But now researchers from Heidelberg, Germany, report in the Annals of Internal Medicine that colonoscopy is indeed a powerful way of detecting colon cancer, potentially putting to rest questions about the best way to screen for the disease.
In the study, researchers compared colon cancer rates among 1,688 patients with colon cancer to 1,932 healthy control participants. After adjusting for factors that could influence colon cancer, such as medical history and preventive behaviors such as use of anti-inflammatory drugs, the scientists found that volunteers who have had a colonoscopy in the 10 years preceding the study lowered their risk of colon or rectal cancer by 77%. What’s more, the study also found that this benefit extended to cancers found along the entire length of the intestines, including the harder-to-reach right-side (which is farthest from the rectum, where the colonoscopy starts). Volunteers who had been screened with a colonoscopy lowered their risk of having cancer in the right side of their colon by 56% compared to those who had not opted for the test. (More on Time.com: Healthland’s Guide to Life 2011)
The results confirm the benefit of regular colonoscopy screening, say the authors, and should lay to rest recent doubts about colonoscopy’s value in detecting distal, or right-sided cancers. Two recent studies have questioned the test’s added value in finding tumors in comparison to other available screening methods. While the National Polyp Study, conducted in the U.S. in 1993, found anywhere from a 76% to 90% reduction in colon cancer risk among those who were screened with colonoscopy, studies in Canada and Germany found only a 30% to 50% reduction in risk. These studies also documented no risk reduction from detecting tumors in the right side of colon. What’s more, a U.K. trial found that sigmoidoscopy, which is not as invasive as a colonoscopy and views only the parts of the colon nearest to the rectum, lowered colon and rectal cancer risk by about the same amount, by 33%.
So is a colonoscopy worth the added expense, risk of perforation and discomfort? Experts say, yes, and the German trial supports their conviction. While the current study shows that colonoscopy detects left-sided cancers better than right-sided ones, Dr. David Weinberg, chairman of medicine at Fox Chase Cancer Center, who wrote an editorial accompanying the study, says that some of the discrepancy may be due to differences in technician skill. The quality of the medical preparation of the patient for the test, as well as the operator’s skill in exploring the colon, particularly the right-sided regions, may influence the number of lesions that the test picks up. The study authors, for example, found that colonoscopy was most effective in lowering cancer risk when performed by physicians who detected a high number of polyps, or suspicious growths that could become malignant. These lesions are difficult to detect in the right side of the colon, says Weinberg, since they appear flatter than those on the left side and are easy to miss. (More on Time.com: Explaining Why Meditators May Live Longer)
“The reason I think the current paper is useful is that it suggests that under the right circumstances, well-done colonoscopy in fact offers considerable protection against cancer in both the right side of the colon as well as the left side,” he says. No test available today is 100% accurate in detecting potentially troublesome growths, he adds, and no test may ever be that accurate. It’s been known that even removing polyps from the right side of the colon does not lower risk of cancer as much as eliminating them from the left side of the intestines, and the reason may have to do with the biology of the tumors. “Either the speed at which they grow or the shape they take makes it harder to detect growths on the right side,” says Weinberg.
Dr. Leonard Saltz, head of colorectal oncology at Memorial Sloan Kettering Cancer Center in New York City, notes that the right side of the colon becomes “wider and sloppier.” The diameter of the right portion of the intestines is larger than the left, and that means more crevices, folds and other convolutions that can harbor abnormal lesions. More work needs to be done to clarify why right- and left-sided tumors differ, but in the meantime, the new study highlights the need for professional groups to come up with guidelines that help patients determine how skilled their colonoscopist may be. Making a hospital’s or physician’s average rate of detecting polyps, says Weinberg, may be a start, since it’s a good proxy for how careful a physician may be in scanning colon tissue for potentially dangerous growths.
Even without such information, it’s important to follow current advice about regular colon screening. “Colonoscopy is true cancer prevention,” says Saltz. “It can identify areas at high risk of cancer to start, and remove those areas before cancer starts. The purpose of colonoscopy is not to find early cancer, but to prevent cancer for happening at all, and the test has the ability to do that.” Weinberg echoes that message, adding that “Hopefully this study will help to keep people’s expectations realistic about how well the test works, but also remind them that it works a whole heck of a lot better than doing nothing.”