Sigmoidoscopy Screening Misses Cancer More Often in Women Than in MenKey Words
Colon cancer, rectal cancer, screening, colonoscopy, flexible sigmoidoscopy. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Summary
Researchers comparing two common methods of screening symptom-free patients for signs of possible colorectal cancer found that colonoscopy (which examines the entire colon) was more effective than flexible sigmoidoscopy (which examines only the first third of the colon) – a finding supported by other studies. However, the researchers also found that the less-invasive sigmoidoscopy missed two-thirds of tumors or potential tumors in women, twice as many as it missed in men.
Source
The New England Journal of Medicine, May 19, 2005 (see the journal abstract).
Background
After lung cancer, colorectal cancer causes more cancer deaths in the United States than any other type. Overall, more than 145,000 cases will occur in 2005 and 56,290 people are expected to die from the disease.
People aged 50 and older commonly develop small growths on the inner wall of their colon or rectum that may or may not turn into cancer. Most of these growths (also called “neoplasia”) are benign and will never become cancerous, but some are likely to.
There are a variety of methods used to screen (check) patients for advanced colorectal neoplasia. They differ in terms of how effectively they detect signs of cancer, and also in terms of safety, invasiveness, and cost. Current U.S. guidelines call for men and women at average risk for colorectal cancer to be screened every year beginning at age 50, using whatever method is deemed appropriate in consultation with their doctor. If the result of a screening test is abnormal, the guidelines generally recommend a more definitive evaluation by colonoscopy .
Colonoscopy is the most effective screening tool but it is also the most invasive and expensive: a flexible tube fitted with a light and video camera is inserted through the full length of the colon (also called the large intestine), which winds through the lower abdominal cavity for about six feet.
Less effective but also cheaper and safer is flexible sigmoidoscopy, which also inserts a lighted tube into the colon but less than half as far, leaving the upper (proximal) part of the colon unexamined. Both methods risk puncturing the colon, but the risk is somewhat greater for colonoscopy.
Policymakers have not recommended a “colonoscopy for all” approach to screening because it is expensive, invasive, associated with a slightly higher risk of side effects, requires sedation, and would be difficult to use as the only test for the millions of people who should be screened. Instead, they would like to find a way of identifying which groups would most likely benefit from colonoscopy.
In 2001, researchers reported the results of a large colorectal cancer screening study called the Veterans Affairs (VA) Cooperative Study 380 (see the journal abstract). More than 3,000 symptom-free participants between the ages of 50 and 75 enrolled in the study. Researchers used colonoscopy to determine the number and location of cancerous neoplasia in the participants’ colons, and reasoned that many of the growths would not have been detected using the less-invasive sigmoidoscopy. However, 97 percent of the study participants were men. The following was a tandem study, specifically designed to see whether similar results would be found in women.
The Study
Between 1999 and 2002, researchers at four military medical centers enrolled a total of 1,463 symptom-free women between the ages of 40 and 79. Most were at average risk for colorectal cancer; 16 percent had a family history of the disease. As in the men’s study, researchers performed colonoscopies only, noting the number and location of any advanced neoplasia.
Then, looking only at the women in whom advanced neoplasia was found, the researchers made a clinical judgment as to whether, had sigmoidoscopy been used, the less invasive test would have found the cancerous growths. This comparison group also included women where the sigmoidoscopy – while not able to see the advanced neoplasia themselves – would likely have detected clinical signs that would have required a follow-up colonoscopy.
Researchers then compared these results with data from VA Cooperative Study 380, using men matched to the women in terms of age and risk characteristics.
The study’s lead author was Dr. Philip Schoenfeld, M.D., from the University of Michigan School of Medicine and the Veterans Affairs Center for Excellence in Health Sciences Research.
Results
Advanced neoplasia were detected in 72 (4.9 percent) of the 1,463 women. Of these, researchers determined that only 25 (1.7 percent, an absolute difference of 3.2 percent) would have been diagnosed as having advanced neoplasia if they had been screened with sigmoidoscopy alone.
In other words, 47 of the 72 women (64.8 percent, or two-thirds) who actually had advanced colorectal neoplasia would have been told there was nothing to worry about if examined by sigmoidoscopy alone. The comparable percentage of men who would have been falsely diagnosed from VA Cooperative Study 380 was 33.7 percent – half that of the women. Researchers didn’t know what accounted for the gender difference.
Comments
The study shows that “the majority of cases of advanced neoplasia in women would be missed if they underwent flexible sigmoidoscopy alone,” said the authors. The same conclusion applies to the men’s study, though there the number missed was about one third, compared to twice that number in women. The authors acknowledged “that the implementation of national and international screening programs may be constrained” by the lack of insurance coverage and insufficient resources to meet the demand, but concluded that “in our opinion, colonoscopy is the preferred method of colorectal-cancer screening in average-risk, asymptomatic women.”
“In many areas of medicine, practice runs ahead of definitive data,” said Ernest Hawk, M.D., M.P.H., director of the National Cancer Institute’s Office of Centers, Training, and Resources. “Increasingly, where it is available and when they can afford it, Americans are choosing colonoscopy for colorectal cancer screening. The VA Cooperative Study 380 suggests that colonoscopy detects more advanced neoplasia in men, and now we have evidence that the same is true for women.”
However, said Hawk, a wide variety of factors influence – and sometimes dictate – the choice of screening regimen. “What matters most is that people over 50 years of age get screened by one of the available methods, and that higher risk individuals start being screened earlier,” he said, noting that only one half of such patients do get screened.
Limitations
Hawk cautioned that both of these studies were designed primarily to look for successful detection of colorectal neoplasia, and do not provide a good picture of the risks associated with colonoscopy. “What about the 80-year-old who is not a good candidate for anesthesia?” Hawk asked. “Flexible sigmoidoscopy may be preferred in that instance, so it is important to offer patients a range of viable options.”
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