Despite the fact that screening colonoscopy is advised for adults ages 50 and older, there is not much scientific data to bolster recommendations for how often to undergo the test. The major medical groups recommend colonoscopy every 10 years for people ages 50 and older who are considered at low risk for colon cancer. In general, people who are at high risk, such as those with previous precancerous lesions, should undergo screening every three years.
A new study based on a mathematical model of incidence of the disease, effectiveness of the test and the costs and complications of testing suggests that the standard recommendations are probably on target.
Researchers from the University of Michigan and Ann Arbor VA Health Services found that screening high-risk people every three years and low-risk people every 10 years is effective in reducing colon cancer cases and deaths, although it costs more than conducting no screening whatsoever. Screening low-risk people every five years is much more costly but only marginally more effective. Screening low-risk people every three years,- which some doctors do to avoid lawsuits arising from "missed" colon cancer, is not only not cost-effective but is potentially harmful due to the increased incidence of complications from the test.
However, the authors said, more research is needed to better clarify who is at high- or low-risk in order to sharpen the guidelines even further.
"There is evidence that we are overusing colonoscopy in low-risk patients and under-using colonoscopy in high-risk patients," the lead author of the study, Dr. Sameer Dev Saini, said in a news release. "We need to focus our efforts on high-risk patients, who have the most to gain from these procedures."
Late last year, changes were recommended to both mammography and Pap smear cancer screening tests. It's quite possible that today's recommendations for colonoscopy will also change at some point. For example, better technology shows that some colon cancers are flat or depressed lesions that may go undetected. As more is learned about the disease and screening technology improves, recommendations for screening will be subject to ongoing debate, Saini said.
The study was released Monday in the journal Gastroenterology.
— Shari Roan
Photo: The flexible colonoscopy tube holds a fiber-optic lens through which a physician can see inside the body. Credit: Robert Durell / Los Angeles Times.