Those new guidelines from the American College of Physicians are generally in line with recommendations from other national organizations such as the United States Preventive Services Task Force and the American Cancer Society.

"We all know that it's a very effective screening intervention," said Dr. Amir Qaseem, the lead author of the new guidelines and head of clinical policy at the ACP. "But the percentage of adults getting screened is still on the low end."

While there's evidence that screening can prevent people from dying of colon cancer when it's done correctly, screening also comes with risks -- such as bleeding and punctures of the intestines with colonoscopy -- without any additional benefit when it's done too often or otherwise unnecessarily.

The new guidelines call for screening starting at age 50 in average-risk people and stopping at age 75 or when patients aren't expected to live at least another decade because of other health conditions.

Patients and their doctors can choose between colonoscopy screening once every 10 years, sigmoidoscopy every five years or an annual stool blood test, researchers wrote Monday in the Annals of Internal Medicine.

"We suggested that the risks and benefits of the different strategies varied and that people should be able to choose the strategy that's best for them," said Dr. Michael LeFevre, co-vice chair of the USPSTF, who didn't participate in the new guideline writing. "That remains true."

One recent study suggested that while stool tests may be just as good as colonoscopy at detecting colon cancer, more research will be needed to see if they are equally effective for preventing deaths from the disease (see Reuters Health story of February 22, 2012).

In people with a higher risk of colon cancer because a close relative had the disease, for example, the ACP recommends screening starting at age 40 -- or a decade before the youngest relative was diagnosed -- and using colonoscopy every five years.

"If you have a family history especially, you need to bring it to the attention of your physician," Qaseem advised in a phone interview with Reuters Health.

While under-screening is a problem among certain groups, so is over-screening -- especially among the oldest patients, according to Dr. James Goodwin, a geriatrician who has studied colon cancer screening at the University of Texas Medical Branch, Galveston and wasn't involved in the new research.

"The development of colon cancer... occurs over many, many years," said Goodwin, who told Reuters Health that polyps caught by screening take 15 to 20 years to grow into a symptomatic cancer, on average.

"There's a price to be paid for colonoscopy. It's a small price but it's a big enough price that sooner or later that outweighs the benefit," he said of the potential side effects.

"The thinking is that at age 75 and older, the benefits are small and the harm hasn't decreased -- in fact it's increased."

According to the Centers for Disease Control and Prevention, about 143,000 people in the U.S. were diagnosed with colon and rectal cancer in 2007, the most recent year with data, and 53,000 died of it.

LeFevre said that his impression is that while colon cancer screening has become more widespread in recent years, there are still many people who are eligible for screening and could benefit but are skipping out.

"We have good science to support reduction in colon cancer deaths from the use of screening," he told Reuters Health.

"Don't let fear of colonoscopy keep you away from being screened -- there are other alternatives."

SOURCE: bit.ly/atTzv0 Annals of Internal Medicine, online March 5, 2012.

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