A stool DNA test is a relatively new approach for colon cancer screening. Instead of looking for blood in the stool (like FIT or guiac FOBT), these tests look for certain DNA mutations caused from cancerous tumors or precancerous polyps. Cells from precancerous and cancerous lesions with these mutations are often shed into the stool, where these tests may be able to detect them, therefore indicating the presence of precancerous polyps or colon cancer.
Because DNA mutations may differ between colon cancers, stool DNA tests typically target multiple markers to achieve high detection rates. Also, because DNA markers may be present in only trace quantities in stool, very sensitive laboratory methods are required. The new stool DNA tests demonstrate high detection rates of early-stage colon cancer. Unlike other noninvasive tests, the new stool DNA tests also can detect precancerous polyps.
Only one stool DNA test is currently available in the U.S., but it has not been approved by the Food and Drug Administration (FDA). Next-generation stool DNA tests that have much improved detection rates are undergoing final clinical validation in a multicenter study by the FDA.
Stool DNA testing has been endorsed in the past by the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer and the American College of Radiology, but not by the U.S. Preventive Services Task Force.
Exact Science’s ColoSure™ is the only currently available DNA stool test in the U.S. ColoSure™ can be a useful alternative for asymptomatic patients who are at average risk for developing colon cancer and who are unwilling or unable to undergo a colonoscopy. You should talk to your doctor to see if ColoSure™ makes sense for you to use.
Stool DNA testing requires little preparation. You can eat and drink normally before the test and continue your current medications. There's also no need to empty your colon ahead of time.
The stool DNA test that's currently available isn't approved by the FDA, but it may be prescribed by a doctor under special rules. You'll receive the stool DNA test kit for collecting and submitting your stool sample at your doctor's office or by mail if you order it online. The kit includes a container that attaches to the toilet. After you collect the stool sample, you either return the kit to your doctor or mail it to the lab. The test requires only one sample.
Various methods to improve the ease of stool collection and sampling are under evaluation. The stool DNA test may be repeated every two to five years, but additional research must be done to determine the optimal interval for testing. In addition, Medicare currently doesn't cover the test, but some private insurers do.
Your doctor will review the results of your stool DNA test and then share the results with you.
Negative result: A test is considered negative if DNA markers common to colon cancer or precancerous polyps are not found in your stool.
Positive result: A test is considered positive if DNA markers common to colon cancer or precancerous polyps are found in your stool sample. In this case, additional evaluation — usually colonoscopy — would be recommended to determine whether you have cancerous or precancerous changes in your colon or other parts of your digestive system.
False-negative result: A false-negative result — a negative test result when cancer is present — may occur if colon cancer or polyps do not harbor DNA markers targeted by the stool DNA test, or if markers are present in extremely low amounts. While next-generation stool DNA test methods appear to be capable of detecting most colon cancers and precancerous polyps, further study is needed to determine what the rate of false-negative results will be.
False-positive result: A false-positive result — a positive test for cancer when no cancer is present — may occur in about five to ten percent of people screened. False-positives could be due to the presence of tumors above the colon or to a problem with the test. When the stool DNA test result is positive but a follow-up colonoscopy is normal, your doctor may recommend further observation with another stool DNA test, evaluation of your upper gastrointestinal tract, a repeat colonoscopy or a combination of these. Research is being done to clarify the best way to manage false-positive results
For more information about sDNA, please call the Colon Cancer Alliance’s Toll-free Helpline at (877) 422-2030.