New Test May Ease Colorectal Cancer Screening

A new, noninvasive screening test for colorectal cancer (search) may encourage more people to get tested for the deadly and often silent disease.

New research shows that the experimental test, which screens for genetic mutations associated with colorectal cancer found in stool, is more effective at detecting cancers and precancerous growths than the only currently available noninvasive test, fecal occult blood stool testing (search) (FOCB).

While neither of these noninvasive screening tests approaches the detection accuracy of a colonoscopy, researchers say the easy-to-administer test may offer a new alternative for colorectal cancer screening.

"A simple, noninvasive test that detects tumor-specific products with reasonable sensitivity and specificity might overcome barriers to screening among persons who are not willing to have a more invasive test, such as colonoscopy," says researcher Thomas Imperiale, MD, professor of medicine at the Indiana University School of Medicine, in a news release.

Although colorectal cancer is the second leading cause of cancer death among adults and recommendations exist that encourage screening for all adults over 50, researchers say less than 40 percent of people aged 50 years or older are screened for colorectal cancer.

"There are many reasons why people don't get screened for colon cancer," says Imperiale. "Some individuals do not want colonoscopy because of discomfort, despite conscious sedation, its inconvenience, or its risk for complications; others are unwilling to smear stool samples on a card for the occult blood test every year."

New Option in Colorectal Cancer Screening On the Way

In the study, which appears in the Dec. 23 issue of The New England Journal of Medicine, researchers compared the rates of fecal DNA testing with FOCB in detecting colorectal cancers or precancerous growths (polyps) in more than 2,500 men and women over age 50 considered to be at average risk for colorectal cancer.

Previous studies have shown the fecal DNA testing was effective at detecting cancers and precancerous growths in people at high risk for the disease, but researchers say this study is the first to test fecal DNA detection rates in large numbers of people at average risk.

The fecal DNA test screens for 21 different genetic mutations associated with colorectal cancer found in stool. It requires a single stool sample, which is expelled from the body directly into a container.

The results showed that the stool screening test was four times more sensitive than the FOCB test in detecting invasive colorectal cancers and more than twice as sensitive in detecting precancerous growths.

Researchers say the fecal occult blood test found only 13 percent of colorectal cancers while the fecal DNA test found 52 percent, as verified by colonoscopy.

The fecal DNA testing detected 13 cancers that were missed by FOCB, while the FOCB detected one cancer that was missed by the fecal DNA test.

Researchers say FOCB testing is less accurate because it screens only for blood found in the stool that is secreted by cancerous or precancerous growths. But most cancerous growths bleed only intermittently and many precancerous growths do not bleed at all.

Previous studies have shown that precancerous and cancerous colorectal growths shed abnormal DNA, which is detectable in stool, and this test is designed to screen for those abnormalities.

Researchers say most precancerous growths that were detected by colonoscopy were not found by either test, but the stool DNA test found more of these growths than the FOCB test.

The stool DNA test has not yet been approved by the FDA for widespread use in colorectal cancer screening. But researchers say the results indicate that the test may be valuable as a more frequent screening tool to be used in combination with more accurate tests that are used infrequently, such as colonoscopy.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Imperiale, T. The New England Journal of Medicine, Dec. 23, 2004; vol 351: pp 2704-2714. News release, Indiana University.