Colon Cancer Screenings Work: Colonoscopy, Other Tests Reduce Cancer Risk By Up To 56%

colon cancer
A pair of studies has proven that colon cancer screenings are far more effective at reducing a person's risk for cancer than abstaining from testing entirely. TipsTimes, CC BY-SA 2.0

Observing personal responsibility when it comes to your health is often difficult. It’s made even more difficult when doctors ask you to receive one test every 10 years. Long gaps between each screening may make them seem arbitrary, but when it comes to colon cancer screenings, the fact is these tests are proven effective at lowering your risk for cancer.

Doctors recently outlined three procedures that can decrease your risk for developing colon cancer by up to 56 percent: colonoscopies, sigmoidoscopies, and fecal blood tests. Each is less invasive than the one before it, yet comes with more frequent testing. A person who receives a colonoscopy every 10 years can expect the same relative level of safety as a person who has doctors check his or her stool samples for blood once a year. No matter the screening option, researchers said the benefits of testing far outweigh the risks of receiving no tests at all.

Pick Your Procedure

Colonoscopies still remain the most effective way to check for colon cancer, according to a recent study published in the New England Journal of Medicine. At 56 percent risk reduction, the procedure tops sigmoidoscopies (40 percent) and occult blood tests (32 percent) as the most trusted way to detect early signs of colon cancer primarily because of its thoroughness. Colonoscopies involve doctors running a thin, flexible tube, equipped with a camera, through the entire length of the patient’s colon. Patients are normally sedated for the procedure.

Sigmoidoscopies use a shorter, flexible tube that doesn’t penetrate as far into the colon. Patients are typically awake during the procedure. Both offer significant benefit to the patient, asserts Dr. Andrew Chan, an assistant professor at the Massachusetts General Hospital Gastrointestinal Unit and the co-senior author of the report.

"Colonoscopy was superior to flexible sigmoidoscopy in terms of reducing the risk of colon cancer throughout the colon," Chan told HealthDay. "But this study really does support the existing guidelines and recommendations for individuals to undergo screening with either colonoscopy or sigmoidoscopy. I think this study shows there's a very real impact on the risk of developing cancer and dying of cancer."

Chan and his colleagues noted in their report that the two procedures, while effective at detecting and preventing colorectal cancer, cannot reliably predict the magnitude or duration of the protection — “particularly of the proximal colon,” they wrote, referring to the deepest part of the colon.

Funded by the National Institutes of Health, the study included nearly 89,000 patients over the span of 22 years. In that time, doctors observed 1,815 cases of colorectal cancer and 474 deaths. People were diagnosed with cancer within five years of their colonoscopy more frequently than after that period or without the screening at all, the report states.

The Benefits Of Choice                                        

Part of what makes these screening options more attractive as a bundle is their varied approach to diagnosing cancer. Due to their invasiveness, colonoscopies require patients to flush out their colon completely the night before the procedure, through fasting and the use of heavy laxatives. If that presents too much discomfort for a patient, he or she can opt for a less invasive method. Some choice is better than none, the researchers argue.

"Quite honestly, many patients don't have access to colonoscopy or are not willing to undergo a screening colonoscopy,” said Dr. Durado Brooks, director of prostate and colorectal cancers for the American Cancer Society. “Many studies have shown that offering patients options will increase the likelihood that they will complete some form of screening, and that is what is most important."

Brooks added that including the range of options in the guidelines for preventing colorectal cancer “continues to make sense.”

Occult blood tests saw their successes proven in the mid-1970s and into the early 1990s, when researchers from the University of Minnesota followed up in 2008 on patients who received the screening. “Occult” blood tests refer simply to blood that is hidden within the feces and not plainly visible to the patient.

In the study’s follow-up, the research team found among 46,551 patients that annual blood tests lowered the risk for colorectal cancer by 32 percent. Biennial testing saw the effectiveness drop to 20 percent. Patients were screened between 1976-1982 and again between 1986-1992. Researchers concluded that occult blood test has proven effective over 30 years, and some experts argue it’s even better today.

"The old fecal blood test that was done in the Minnesota trial has been improved and enhanced through modern biochemical methods," said Dr. Theodore Levin, a research scientist at the Kaiser Permanente Northern California Division of Research and author of an accompanying editorial to the two studies. "It's much more accurate and much more sensitive, so we would expect the benefit to be even greater today with that test."

Potential Value

With the greater range of choice offered to patients also come potential benefits from procedures that are generally regarded as inferior, Levin added. Colonoscopies are performed less frequently, but require greater patient responsibility to compensate. Inadequately flushing the colon prior to the procedure could hamper doctors’ ability to root out polyps or cancer. Colonoscopies also cannot detect small lesions in the colon.

Indeed, more modest tests performed at greater frequency could be more effective in the long run at “detecting colon cancer or preventing death from colon cancer,” Levin said.

"My hope is people will see these studies and realize there is potential value in all these tests," Brooks added. "Choosing any one of them is far superior to not being tested."

 

Sources: Nishihara R, Wu K, Lochhead P. Long-Term Colorectal-Cancer Incidence and Mortality after Lower Endoscopy. The New England Journal of Medicine. 2013.

Shaukat A, Mongin S, Geisser M. Long-Term Mortality after Screening for Colorectal Cancer. The New England Journal of Medicine. 2013.

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