Stool DNA and Occult Blood Testing to Screen for Colorectal Neoplasia

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The summary below is from the full report titled "Stool DNA and Occult Blood Testing for Screen Detection of Colorectal Neoplasia." It is in the 7 October 2008 issue of Annals of Internal Medicine (volume 149, pages 441-450). The authors are D.A. Ahlquist, D.J. Sargent, C.L. Loprinzi, T.R. Levin, D.K. Rex, D.J. Ahnen, K. Knigge, M.P. Lance, L.J. Burgart, S.R. Hamilton, J.E. Allison, M.J. Lawson, M.E. Devens, J.J. Harrington, and S.L. Hillman.

What is the problem and what is known about it so far?

Colorectal cancer arises from the lining of the colon. It causes more deaths than any other type of cancer except lung cancer, but it is curable if detected and removed before it spreads to other organs. Fortunately, colon cancer develops from growths called polyps, which do not spread to other organs but are detectable by imaging tests, such as radiography; inspecting the surface of the colon through a flexible tube (colonoscopy); and testing the stool for substances released from polyps and cancers. Polyps take 5 to 10 years to become cancerous. Abnormalities in DNA from cells in a polyp cause the cells to lose control of division, which allows the polyp to become larger. Additional DNA abnormalities occur that allow cancer cells to invade the rest of the body. Polyps and cancer constantly shed cells into the stool, and it is possible to detect the mutations that cause polyps to grow and become malignant. The tests are called stool DNA tests.

Why did the researchers do this particular study?

To see whether stool DNA tests detected more polyps and cancers than did tests for blood in the stool, a well-proven colon cancer screening test.

Who was studied?

3764 healthy adults with an average risk for colon cancer.

How was the study done?

The study participants collected samples of stool at home and sent them to a laboratory that tested for hidden blood. Another laboratory tested the stool to see whether it contained DNA abnormalites associated with polyps or cancer. The laboratory used 2 tests, which were designed to detect different gene abnormalities. Everybody had colonoscopy, the most reliable test for colon polyps and cancer.

What did the researchers find?

The best test for blood in the stool detected 21% of the cases of cancer and most worrisome types of polyps. The older of the 2 stool DNA tests (called SDT-1) detected 20% of cases of cancer. The newer stool DNA test (called SDT-2) detected 40% of the cases of cancer and most worrisome types of polyps.

What were the limitations of the study?

The researchers did not measure the frequency of positive SDT-2 tests in all patients who did not have worrisome polyps or cancer (false-positive results).

What are the implications of the study?

Testing stool for DNA abnormalities that control cell growth is a promising way to screen for colon polyps and cancer.