Most experts recommend that people at average risk of colon cancer start having screening tests for the disease at age 50. And there are choices.

The U.S. Preventive Services Task Force, a government-backed body that sets screening guidelines, recommends three options: a yearly stool test that looks for hidden blood; sigmoidoscopy every five years, along with stool testing every three years; or colonoscopy every 10 years.

Other groups, like the American Cancer Society, have similar recommendations.

The reality, though, is that colonoscopy - the most extensive, invasive and expensive of the tests - has become the screening method of choice in the U.S.

"But it shouldn't be one strategy for everyone," said Dr. Thomas F. Imperiale, a gastroenterologist at Indiana University in Indianapolis who led the new study.

One reason, he said, is because colonoscopies deter some people from getting any screening. "There are a lot of people who stay away from colon cancer screening altogether because they equate screening with colonoscopy," Imperiale said. "But there are alternatives."

For their study, Imperiale and his colleagues looked at data on more than 10,000 U.S. adults age 50 and up who underwent a screening colonoscopy. They found that among women younger than 70, only one percent had either a tumor or advanced polyp - a growth that could become cancer - in the upper part of the colon.

That was half the rate seen among men their age. Older adults had the highest risk: nine percent of men and four percent of women older than 70 had a tumor or advanced polyp in the upper colon.

According to Imperiale, the findings suggest that for women younger than 70, sigmoidoscopy could be adequate as an initial colon cancer screening.

Like colonoscopy, sigmoidoscopy uses a long flexible tube equipped with a tiny video camera to see the interior of the colon. The difference is that a colonoscopy gives images of the entire colon, while a sigmoidoscopy looks only at the rectum and lower portion of the colon.

So a sigmoidoscopy can be done relatively quickly - in about 15 minutes - without sedation, and with a lower risk of perforating the colon. It can also be done by primary care doctors or trained nurse practitioners; colonoscopies are usually done by gastroenterologists.

"All we're saying is, with people at average risk of colon cancer, there are some groups who may not need a colonoscopy," Imperiale said.

He and his colleagues report the findings in the American Journal of Medicine.

Dr. Durado Brooks, director of prostate and colorectal cancers for the American Cancer Society, said that the findings are in step with what's already known: The risk of colon polyps and tumors goes up with age, and at any age, women are at lower risk than men.

"We also know that flexible sigmoidoscopy is an effective approach to colon cancer screening," Brooks said.

But even if you want sigmoidoscopy, you'll be hard pressed to find a doctor who does them. "In the U.S., it's a dying art," Brooks said. "The vast majority of centers are only doing colonoscopies."

Why? "Quite honestly, there's a financial motivation," Brooks said. "The reimbursement for sigmoidoscopy is poor."

A sigmoidoscopy gets about $150, versus $1,000 for a colonoscopy. For primary care doctors, Brooks noted, it's not "cost-effective" to even offer sigmoidoscopy.

There are other considerations, though, Brooks said. Because there's no sedation with sigmoidoscopy, it's actually more uncomfortable than colonoscopy.

"And of course there's the potential for missing cancers," Brooks said - though, he added, "colonoscopy isn't perfect either."

Brooks and Imperiale both said it makes sense to move toward "customized" recommendations on colon cancer screening for people at average risk. But more research is needed first.

"There are risk factors other than age and gender," Brooks noted.

Most of the people in the current study, for example, were white. But research suggests that African Americans are at higher risk of colon polyps and cancer. So, Brooks said, it's possible that relatively young black women would have a higher risk of growths in the upper colon, compared with the women in this study.

There's also evidence that obesity and diabetes are risk factors, Imperiale noted. He agreed that more work is needed before recommendations can be refined to suggest certain screening tests for certain people.

"For now, the main message is to get screened starting at age 50," Brooks said. "Any one of these tests is better than not being screened."

"I think that if you don't want a colonoscopy, you should talk to your doctor about alternatives," Imperiale said.

With sigmoidoscopy so out of favor in the U.S., the main alternative you find may be a yearly stool test. But Imperiale said he thinks sigmoidoscopy could make a comeback, as more research confirms its effectiveness; recent trials have shown that the test cuts deaths from colon cancer.

"I think the trend in this country could reverse," Imperiale said, "if we want it to."

SOURCE: bit.ly/S8ddTP American Journal of Medicine, online October 10, 2012.

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