Screening Interval for Colorectal Cancer Questioned

Study finds benefits of sigmoidoscopy can last 10 years or more

TUESDAY, April 15, 2003 (HealthDayNews) -- A new study questions the recommended guidelines for a common colorectal cancer screening procedure, and suggests the current five-year screening interval may be excessive.

The benefits of the procedure, called a sigmoidoscopy, can last as long as 10 or even 15 years, the study researchers say.

Almost 1 million cases of colorectal cancer are diagnosed worldwide each year. Several effective tests are available that can detect the disease in its earliest and most treatable stages, but little is known about how often patients over 50 should undergo these screenings.

Previous studies have shown that precancerous tissue, called polyps, can take up to 15 years to progress to cancer, suggesting that screening may not be necessary as often as every five years.

Researchers from the Fred Hutchinson Cancer Research Center in Seattle looked at the efficacy of sigmoidoscopy screening -- a procedure where a scope is used to examine the lower part of the large bowel -- in reducing the incidence of colorectal cancer. They also asked the question: How often should this test be used for the greatest risk-to-benefit ratio?

The study examined the screening history and colorectal risk factors of 1,668 patients between the ages of 20 and 75 living in Washington state. The researchers compared the rate of colorectal cancer in this group to 1,294 healthy individuals within the same age range.

The findings show those who had received a screening sigmoidoscopy had a fourfold reduction in the incidence of colorectal cancers compared with individuals who had never had the procedure. Moreover, this benefit appeared to be sustained for more than 15 years, indicating the recommended screening interval is too aggressive.

"If screening by sigmoidoscopy every 10 years was widely adopted by adults over age 50, the incidence and mortality of colorectal cancer could be substantially reduced," says Polly Newcomb, a researcher at the Fred Hutchinson Cancer Research Center in Seattle and lead author of the study, which appears in the April 16 issue of the Journal of the National Cancer Institute.

Patients don't like invasive screening procedures such as sigmoidoscopies and compliance is an ongoing problem for physicians. Moreover, if the screening was recommended once every 10 years, the reduction in usage would translate into significant savings for the health-care system, the researchers argue.

But Jack S. Mandel, chairman of epidemiology at Emory University's Rollins School of Public Health, says the structure of the study may undermine its findings.

"There's a tendency for these types of studies to overstate the benefits. We're trying to understand the precise magnitude of the benefit [of sigmoidoscopy screening] and in this study there's uncertainty in that benefit," he says.

The number of individuals involved in some of the study's analyses are so small that they could easily be distorted by a mistake or classification error. Moreover, says Mandel, the study looked at self-reported data that was not verified using patient records to ensure that the subjects had really undergone screening sigmoidoscopy.

That bias tends not to be a problem because sigmoidoscopy isn't a procedure that a patient is likely to forget, Newcomb says. People rarely confuse it with other screening tests because the experience is unique from the other available options, she says.

Mandel argues a decision to lengthen the recommended five-year sigmoidoscopy screening interval should be postponed until more accurate data are available from a large randomized control trial -- several of which are currently under way.

Newcomb, however, cautions results from those studies are unlikely to be available for another 10 years. In the meantime, the results of studies like this one are the next best thing to a randomized control trial.

More information

Click on the U.S. Centers for Disease Control and Prevention for tips on preventing colorectal cancer. The American Cancer Society has a page explaining both sigmoidoscopy and colonoscopy. Also, try the Cancer Research and Prevention Foundation.

Related Stories

No stories found.
logo
www.healthday.com