For people who are younger than 80 years, the benefits of a colonoscopy might last more than 10 years-the period of time currently recommended before the procedure is repeated. However, this screening, which looks for colon polyps that could become cancerous over time, may provide only a minimal benefit to people who are age 80 or older.

The First Study

The first study, conducted by researchers at the University of Manitoba in Winnipeg, Canada, looked at data on nearly 35,000 Canadians whose colonoscopies found no polyps. During the next 10 years, the incidence of colon cancer in these individuals was 72% lower than in the general population, the researchers report. In addition, the decreased risk of colon cancer continued for more than 10 years.

Although the Canadian team did not call for a change in the recommended screening interval, the researchers did say that the "findings suggest that screening colonoscopies do not need to be performed at intervals shorter than 10 years."

The second Study

The second study, conducted at Virginia Mason Medical Center in Seattle, looked at colonoscopies that were performed on 1,244 people in three age groups-50 to 54; 75 to 79; and 80 and older.

The incidence of colon cancer was much higher in the oldest participants-14% for the 80-and-older group-compared with 3.2% for the 50-to-54-year-old group. However, the study found that colonoscopy does not significantly extend the life expectancy of people older than 80 years-it increased survival only by approximately 45 days for the oldest group, compared with more than 10 months for people ages 50 to 54.

The results "suggest that the benefit of screening colonoscopy in very elderly patients may be smaller than what is commonly believed," the researchers say. They add that the information might "help avoid its use in patients who are unlikely to benefit substantively."

Looking At The Results

Both studies were observational, and neither is definitive, says Timothy R Church, a professor of environmental health sciences at the University of Minnesota School of Public Health in Minneapolis.

He agrees that the Canadian study "doesn't give us any reason to change the currently recommended interval of 10 years. [However,] it does leave open the possibility that an even longer interval might be possible."

The Seattle study, he says, "raises a legitimate question: when should you no longer screen for colorectal cancer?"

The answer, of course, would involve more factors than just age, Church says. "The decision needs to be based not strictly on age, but on the health of the individual. Some older people are in good shape and will live for 20 years or more. Others have multiple health problems-their hearts or other organs may be failing. They are Likely to die of something other than colorectal cancer, so we definitely need to take into account what a person's health status is before making a screening decision," he explains.

"For this age group we have to be extra careful," agrees Dr. Stephen Shibata, director of the gastrointestinal program at the City of Hope Cancer Center in Duarte, California. "We need to know what the patient's health is, what the patient wishes. The patient and the physician need to have a discussion before they [decide on] a procedure."

"The big issue is identifying those people in whom the benefit [of colonoscopy] outweighs the risk," says Robert A. Smith, director of cancer screening for the American Cancer Society.

Other, less uncomfortable screening techniques, such as fecal occult blood tests (FOBT) and flexible sigmoidoscopy, may also be effective, Church adds.

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