Sigmoidoscopy comes up short for women in detection of polyps in the colon

May 20 2005

A new multi-center study has reaffirmed the difference between the sexes – at least when it comes to colorectal cancer detection and prevention.

In the first large-scale study involving women, researchers from the University of Michigan, the National Cancer Institute, the University of Minnesota Cancer Center, the National Naval Medical Center and the Walter Reed Army Medical Center found that colonoscopy is the preferred colon cancer screening method in average-risk women because other screening tools would miss most advanced pre-cancerous polyps.

The results from the CONCeRN (COlorectal Neoplasia screening with Colonoscopy in average-risk women at Regional Naval medical centers) study team of investigators appear in the May 19 issue of the New England Journal of Medicine.

Previous research on colon cancer screening using colonoscopy focused primarily on men, including the Veterans Affairs Cooperative Study 380 that evaluated more than 3,000 patients - 97 percent of whom were male. This research determined that fecal occult blood testing (which identifies microscopic amounts of blood in stool) and flexible sigmoidoscopy (which examines the lower 25 percent of the colon) would identify more than 70 percent of men with advanced pre-cancerous polyps.

While these tools miss approximately 30 percent of advanced pre-cancerous lesions in men, their utility in women has not been adequately tested and many health care providers offer only fecal occult blood testing or flexible sigmoidoscopy for colon cancer screening for both men and women. However, based on the results from the CONCeRN study, colonoscopy is clearly the preferred colon cancer screening method for women, says lead author Phillip Schoenfeld, M.D., assistant professor in the Division of Gastroenterology in the Department of Internal Medicine at the University of Michigan Medical School.

"With heart attacks and other diseases, we know that men and women develop symptoms differently and require different approaches – and colon cancer screening should be no exception," says Schoenfeld, also with the Division of Gastroenterology, Uniformed Services University of Health Sciences.

"While fecal occult blood testing and flexible sigmoidoscopy are less expensive, faster and require no sedation, 65 percent of women with advanced pre-cancerous polyps in our study would have lesions missed if these were the only screening tests performed because pre-cancerous polyps are found deeper in the colon in women."

The reason: men and women do not develop polyps in the same area of the colon, a finding that surprised Schoenfeld and his colleagues. The study revealed advanced pre-cancerous polyps in men tend to grow in the lower portion of the colon, whereas women's polyps tend to grow deeper in the colon, beyond a flexible sigmoidoscopy's reach.

To determine the most reliable screening method for average-risk women, the CONCeRN study looked at 1,483 consecutive average-risk, asymptomatic women, ages 50 to 79, who had been referred for colorectal cancer screening at four military medical centers: the National Naval Medical Center in Bethesda, Md., the Walter Reed Army Medical Center in Washington, D.C., and Naval Medical Centers in San Diego, Calf., and Portsmouth, Va. After patients had a negative fecal occult blood test of their stool, they were offered a colonoscopy instead of flexible sigmoidoscopy.

During the colonoscopy, the location of all polyps was defined based on the depth of insertion of the colonoscope and anatomical landmarks. To quantify the diagnostic ability of flexible sigmoidoscopy, researchers used colon landmarks to determine which lesions would have been found with flexible sigmoidoscopy.

Using the male patients from Veterans Affairs Cooperative Study 380 and the female patients from the CONCeRN study, Schoenfeld and his colleagues compared the diagnostic ability of flexible sigmoidoscopy and the prevalence of advanced pre-cancerous polyps in men and women. Patients from both studies were matched based on risk factors including age, negative fecal occult-blood test, and the absence of a family history of colon cancer.

In the study, men were twice as likely to have advanced pre-cancerous polyps as women: 8.6 percent vs. 4.9 percent. However, if only a flexible sigmoisdoscopy had been performed in the women, advanced pre-cancerous lesions would have been identified in only 1.7 percent and missed in 3.2 percent, says Schoenfeld.

"Our study found that the sigmoidoscopy results told us little if anything about the health of the colon beyond the lower one-quarter reached by the sigmoidoscope," says co-author Andrew Flood, Ph.D., epidemiologist at the University of Minnesota Cancer Center and School of Public Health. "To detect polyps in the upper or proximal portion of the colon, which is where about two-thirds of the polyps found in study participants were, we need to rely on colonoscopy."

These results also reinforce two key messages: "First, medical research conducted in men cannot routinely be applied to women. Women may be at a disadvantage if medical research is focused on men because women have unique biological differences that may require different diagnostic tools or treatments. Second, both men and women need to get a colonoscopy after the age of 50, when polyps slowly begin to grow and can be easily removed during a colonoscopy," says Schoenfeld.