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New At-Home Colon Cancer Test: FAQ

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WebMD Health News

Aug. 13, 2014 -- A new at-home colon cancer test that looks for DNA mutations in stool is more accurate than the stool test currently used, but it won’t replace colonoscopies, experts say.

The test, called Cologuard, is "another weapon in our arsenal for colon cancer screening," says James Lin, MD. He's a clinical assistant professor of gastroenterology at the City of Hope Comprehensive Cancer Center.

''Colonoscopies are still the gold standard," says Peter Galier, MD. He's a professor of medicine at UCLA Medical Center, Santa Monica. In a colonoscopy, a flexible, lighted tube is used to examine the colon and rectum for anything usual.

Galier says the question that needs to be answered about the $599 Cologuard test is: How cost-effective is it?

WebMD asked these two experts -- who have no ties to the company making Cologuard -- and the test maker for more details.  

More than 137,000 new cases of colon or rectal cancer are expected to be diagnosed this year, according to the American Cancer Society. Early detection improves survival.

How does the test work?

Cologuard looks for mutations that have been linked with colorectal cancer in the blood and DNA of cells shed in the stool.

You don't have to restrict your diet or prep your bowel by drinking a large amount of liquid to make you go to the bathroom before the test, as before a colonoscopy.

You receive a collection kit that you use to collect two stool samples, one for DNA testing and one for blood testing. These samples are sent to a lab for processing and testing, which takes about 2 weeks. Your doctor gets the results.

How does it differ from other stool-based tests?

Other stool tests, including the fecal occult blood test (FIT) and fecal immunochemical test, work by detecting tiny amounts of blood in the stool that could indicate cancer or large polyps, growths that can develop into cancer. The other tests don't look at DNA.

How accurate is the new test?

According to the FDA, Cologuard spotted more cancers than the FIT test -- 92% of cancers compared to 74% by the fecal occult test -- in studies that included more than 10,000 people.

Cologuard was also better than the FIT at finding pre-cancerous growths. It detected 42%, while FIT found 24%.

The downside, though, is that the new test was not as good at finding “true negatives.” (A negative test result means the disease being tested for was not found.) Cologuard correctly identified a negative result in 87% of patients, the FDA says, but FIT did so in 95%.

Will the new test replace other tests or supplement them?

It won't replace other tests, but will be another option, experts say. If the test result is positive from Cologuard, a colonoscopy is then needed.

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