After lung cancer , colorectal cancer is the second most common cause of cancer death in the United States. Colorectal cancers begin as polyps, which are small growths of tissue in the colon or rectum (the latter part of your digestive system). While most polyps are benign, they have the potential to eventually turn into cancer. Identifying and removing polyps before they turn into cancer reduces the risk of dying from colorectal cancer.

Current recommendations on colorectal cancer screening indicate that both flexible sigmoidoscopy and colonoscopy are appropriate screening methods for most people without symptoms. Flexible sigmoidoscopy involves the insertion of a thin, lighted, flexible tube into the rectum so doctors can view the last third of the large intestine. Colonoscopy is similar, but uses a longer tube to view the entire length of your large intestine.

Flexible sigmoidoscopy does not require sedation, and is faster and less expensive than colonoscopy, so some researchers have suggested that flexible sigmoidoscopy should be the preferred method of colorectal cancer screening in average-risk people. However, since the majority of colorectal cancer screening research to date has focused on men, it is not clear whether flexible sigmoidoscopy is the appropriate choice for women.

A new study in the May 19, 2005 issue of the New England Journal of Medicine investigated whether flexible sigmoidoscopy would be an effective alternative to colonoscopy in women without symptoms. The researchers found that flexible sigmoidoscopy would miss 65% of the advanced precancerous polyps that would be detected by colonoscopy.

About the Study

This study included 1,463 women from four military medical centers. The women were 50-79 year old, had no symptoms of colorectal cancer, and were at average-risk. In addition, women 40-49 years old could participate if they had a history of colon cancer in a first-degree relative.

None of the women had a history of polyps, colorectal cancer, inflammatory bowel disease, or a genetic polyp disorder. Within six months before the study, each woman had to have a negative fecal occult-blood test (which identifies microscopic blood in the stool).

Gastroenterologists or colorectal surgeons performed colonoscopies on each woman, and recorded the location of all polyps. The researchers categorized all advanced precancerous polyps found in the lower third of the large intestine as polyps that would have been found on flexible sigmoidoscopy alone. In addition, advanced precancerous polyps in the upper two-thirds of the colon accompanied by small polyps in the lower third were classified as polyps that would be found on flexible sigmoidoscopy. This is because the small polyps found on sigmoidoscopy would trigger a full colonoscopy, which would detect the advanced precancerous polyps.

To compare the effectiveness of flexible sigmoidoscopy versus colonoscopy in men, the researchers matched the participants in this study with men from the VA Cooperative Study 380 (which looked at the effectiveness of flexible sigmoidoscopy in men) on the basis of age, a negative fecal occult-blood test, and the absence of a family history of colon cancer.

The Findings

Seventy-two (4.9%) of the women had advanced precancerous polyps, and 227 (15.5%) of them had small or non-advanced polyps.

The researchers determined that if flexible sigmoidoscopy had been performed instead of colonoscopy, only 25 (34.7%) of the advanced precancerous polyps would have been detected.

When the researchers compared the women to the men from the VA Cooperative Study 380, they found that flexible sigmoidoscopy was significantly more accurate in detecting advanced precancerous polyps in men than it was in women. Two-thirds of the advanced precancerous polyps would have been detected in the men with flexible sigmoidoscopy alone.

These results were limited by the fact that the colonoscopies in this study were performed by highly-trained experts, who may have detected more polyps than less experienced colonoscopists practicing in the community.

How Does This Affect You?

These findings suggest that colonoscopy is superior to flexible sigmoidoscopy in detecting advanced precancerous polyps in average-risk women without symptoms. This is important because current recommendations say that flexible sigmoidoscopy is a reasonable substitute for colonoscopy screening in this population.

The results of this study underscore the fact that research in men can not always be generalized to women. Just as women often present with different heart attack symptoms than men, this study suggests that their pattern of early warning signs for colorectal cancer (i.e., advanced precancerous polyps) is distinct from men.

Why is flexible sigmoidoscopy more accurate in men? It’s seems likely that polyps tend to develop deeper in women’s colons, but more research is needed to determine why this is the case. If you are 50 or older, talk to your doctor about scheduling a colonoscopy. You should have the discussion earlier if you have a family or personal history of colorectal cancer or polyps, or have chronic inflammatory bowel disease. If you are a woman and it is financially feasible, push for a colonoscopy, which is apparently your best defense against colon cancer.