By Kathleen Doheny
WebMD Health News
Reviewed by Michael W. Smith, MD
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.
The test is meant for those at average risk of colon cancer, the company says. Even so, there may be a role for it in someone with a family history, Galier says. For instance, a doctor might order it for high-risk people in between regular colonoscopies.
Recent guidelines from the U.S. Preventive Services Task Force, an independent panel of experts, recommend that adults ages 50 to 75 at average risk for colon cancer be screened using fecal occult blood testing, sigmoidoscopy (a more limited exam than colonoscopy), or colonoscopy.
The recommended intervals for each option are annually for fecal occult blood tests, every 5 years for sigmoidoscopy, and every 10 years for colonoscopy, the task force says.
The other question to be answered, Galier says, is how often the Cologuard test is needed. The guidelines have not yet been set up, says Jennifer Netzband, a spokeswoman for the test's maker, Exact Sciences.
Dr. Lin of City of Hope welcomes the new test, saying some patients who avoid colonoscopies may agree to it. "Ultimately the best colon cancer screening test is the one the patient is using," he says.
Cologuard is pricey, compared to the FIT, which is about $30. Will insurance cover it?
That's yet to be determined, Netzband says.
The Centers for Medicare and Medicaid Services (CMS) propose that the test be reimbursed every 3 years for those ages 50 to 85, without symptoms of colon cancer and considered average risk. The decision on that is expected by October or November.
Insurance companies often follow CMS decisions about coverage.
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SOURCES: Peter Galier, MD, professor of medicine, UCLA Medical Center, Santa Monica, and UCLA David Geffen School of Medicine. James Lin, MD, gastroenterologist and clinical assistant professor of gastroenterology, City of Hope Comprehensive Cancer Center, Duarte, CA. Jennifer Netzband, Exact Sciences spokesperson. Press release, FDA. Press release, Exact Sciences. American Cancer Society: "Understanding Tests that Screen for Colon Cancer," "Colorectal Cancer."
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