Colonoscopy may be the "preferred method of screening" for colon cancer and rectal cancer in women, say doctors in The New England Journal of Medicine.

No colon cancer screening test is perfect. It's possible for colonoscopy (or any screening method) to miss some cancers or polyps. However, colonoscopy may be a woman's best test, shows the study by researchers including Philip Schoenfeld, MD, of the University of Michigan's medical school.

Colon cancer is the third most common cancer found in men and women in the U.S. (not counting skin cancer), says the American Cancer Society (ACS). The ACS expects nearly 105,000 new cases of colon cancer, more than 40,000 new rectal cancer cases, and more than 56,000 deaths from both kinds of cancer this year.

Early Detection Saves Lives

The death rate for colorectal cancer has been dropping for 15 years, says the ACS. Early detection can greatly improve chances of survival.

The ACS recommends that men and women of average risk begin screening at age 50. Those with certain risk factors should begin screening earlier, says the ACS.

Screening methods include colonoscopy, "virtual" colonoscopy, flexible sigmoidoscopy, fecal occult blood tests, and double-contrast barium enemas. Other studies have shown colonoscopy detects more cancers.

A colonoscope is a longer version of a sigmoidoscope. It's a thin, lighted tube with a tiny camera that doctors use to look inside the colon. A colonoscope can be guided all the way along the colon. A sigmoidoscope only lets a doctor see about half of the colon, says the ACS.

Latest Colon Cancer Test Findings

Schoenfeld and colleagues studied more than 1,400 women aged 50-79. The women had an "average risk" of colorectal cancer, says the study. A total of 230 women (about 16%) had a family history of colon cancer.

The women filled out detailed questionnaires about risk factors before undergoing colonoscopy.

While everyone is at risk for colon cancer, traditional risk factors for colon cancer include:

--Age. Risk increases with age.

--Sex. Women are at a higher risk for colon cancer while men have a higher risk for cancer of the rectum.

--Family history. Parents, siblings, and children of a person who has had colorectal cancer are somewhat more likely to develop colorectal cancer themselves.

--Diet. Diets high in fat and calories and low in fiber are linked to this cancer.

--Polyps. These noncancerous growths are common in people over the age of 50. A certain type of polyp, called adenomas, is considered precancerous.

The researchers estimated the number of cancers, polyps, and other problems that would have gone undetected if the women had only gotten sigmoidoscopy.

Colonoscopy identified cancers and polyps in 72 women (5 percent). Only 35 percent of those women would have had those lesions identified if they had only gotten sigmoidoscopy, says the study.

Outcome in Men

Researchers had previously done a similar estimate on men. That study affirmed colonoscopy's superiority.

However, the men's study showed that sigmoidoscopy would have identified cancer and polyps in a greater percentage of affected participants (66 percent), say Schoenfeld and colleagues.

"We found that almost twice as many cases of advanced colorectal neoplasia were detected in the men," write the researchers. "Flexible sigmoidoscopy appears to be a much more effective screening tool in men than women."

'Preferred' Screening Method for Women

"On the basis of these data, we believe that colonoscopy is the preferred method of screening for colorectal cancer in women, and that flexible sigmoidoscopy is an inadequate method of predicting advanced neoplasia in the proximal colon in women," write researchers.

The men's results came from the Veterans Affairs Cooperative Study 380. The women's study included women from four military medical centers.

By Miranda Hitti, reviewed by Brunilda Nazario, MD


SOURCES: Schoenfeld, P. The New England Journal of Medicine, May 19, 2005; vol 352: pp 2061-2068. American Cancer Society: "How Many People Get Colorectal Cancer?" American Cancer Society: "How is Colorectal Cancer Found?" WebMD Medical News: "Colonoscopy Best at Detecting Colon Cancer."