Results from a new study of a test that can detect abnormal DNA associated with colon cancer in stool samples received mixed reactions. Many in the medical community and the public have been looking for possible alternatives to the invasive procedure of colonoscopy, the current gold standard in colorectal cancer detection. Although the results did suggest that the DNA test was superior to fecal occult blood testing (FOBT), a simple noninvasive test that detects hidden blood in stool (a potential indication of cancer), they did not demonstrate the test’s ability to outperform colonoscopy.

Published in the December 23, 2004 issue of The New England Journal of Medicine, the study compared the DNA test (a panel of 21 genetic mutations associated with colorectal cancers and precancerous growths) with the Hemoccult II FOBT among several thousand asymptomatic patients age 50 and older who were at average risk for the disease. The DNA test was able to detect 16 out of 31 invasive colon cancers (52%) compared with 4 out of 31 (13%) detected by the FOBT. Both tests had similar specificity (ability to correctly exclude those patients who do not have the disease) of approximately 95%.

The DNA test, however, only detected about half as many colorectal cancers as colonoscopy, which is highly sensitive and can detect almost all cancers or precancerous growths present.

Nevertheless, some are suggesting that the new DNA test could augment colorectal cancer screening through more frequent use of this test in combination with less frequent colonoscopy (see Screening Tests for Adults 50 and Up: Colorectal Cancer). The DNA test requires less direct patient handling of stool than FOBT in addition to its superior accuracy, although its cost is substantially higher than FOBT ($400-$800 compared to $3-$40 for FOBT).

More research is needed to confirm the findings, especially given concerns that the FOBT performed unusually poorly in this particular study. In fact, the sensitivity of FOBT is under scrutiny after the release of findings from another recent study in which researchers discovered that a single-sample FOBT detected only 4.9% of advanced neoplasias among 284 patients when performed once in the doctor’s office and caught 23.9% when the patient performed the 6-sample test at home.

Colonoscopy clearly remains the gold standard for detection of colon cancer, which is more likely to be successfully treated if found early. Researchers are continuing to study ways to improve the sensitivity of the DNA test while further examining the appropriate use and limitations of the FOBT.

Sources
“DNA Test Falls Short in Colon Cancer Trial.” Washington Post, December 23, 2004.

New England Journal of Medicine. Fecal DNA versus Fecal Occult Blood for Colorectal-Cancer Screening in an Average-Risk Population. December 23, 2004. Abstract available online at: http://content.nejm.org/cgi/content/abstract/351/26/2704

WebMD Health. Jennifer Warner. New Test May Ease Colorectal Cancer Screening: Noninvasive Test May Encourage More Frequent Colorectal Cancer Screening. December 22, 2004 http://my.webmd.com/content/article/98/104930.htm

American Cancer Society. ACS News Center. DNA Test Finds More Colon Cancers Than Standard Stool Blood Test. But Neither Test Tops Colonoscopy. 12/23/04

Bloomberg News. Colon-Cancer Test Misses 95% of Cases, Study Shows (Correct) By Michelle Fay Cortez. January 18, 2005