Women younger than 70 have a relatively low risk of abnormal growth in the upper part of the colon - suggesting, U.S. researchers say, that many women can opt for less invasive colon cancer screening.

Most experts recommend that people at average risk of colon cancer start having screening tests at age 50, with three options: a yearly stool test that looks for hidden blood, a test called a sigmoidoscopy every five years and stool testing every three years, or a colonoscopy every ten years.

But the reality is, though, that colonoscopies - the most invasive, extensive and expensive of the tests - has become the screening method of choice in the United States.

"But it shouldn't be one strategy for everyone," said Thomas Imperiale, a gastroenterologist at Indiana University, who led the study that appeared in the American Journal of Medicine, noting that the idea of colonoscopies keep 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," he 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 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, with 9 percent of men and 4 percent of women older than 70 having a tumor or advanced polyp in the upper colon.

According to Imperiale, the findings suggest that for women under 70, sigmoidoscopy -- which uses a long flexible tube equipped with a tiny video camera to see the interior of the colon -- could be adequate as an initial colon cancer screening.

Unlike a colonoscopy, a sigmoidoscopy looks only at the rectum and lower portion of the colon. So it can be done relatively quickly, without sedation, and with a lower risk of perforating the colon.

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

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.

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

Research suggests that African-Americans are at higher risk of polyps and cancer, so Brooks said it's possible that relatively younger black women would have a higher risk.

Imperiale noted that there's also evidence that obesity and diabetes are risk factors, agreeing that more work is needed before recommendations can be refined.

"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."