DNA Screening test
92 percent accurate in identifying patients with colon cancer
69 percent accurate in identifying patients with bowel lesions
Mayo offers alternative to colonoscopy -- though it has its own 'ick' factor
- Article by: Jeremy Olson
- Star Tribune
- March 21, 2014 - 10:18 AM
A new test that requires people to send stool samples in the mail for laboratory analysis is proving nearly as reliable as a colonoscopy in identifying potentially fatal colon cancers.
The DNA screening test, invented at the Mayo Clinic, could become an alternative to the colonoscopy — or at least an option for the millions of Americans who ignore their doctors’ recommendations because they are squeamish about the rectal exam or concerned about its cost, said Dr. David Ahlquist, a Mayo gastroenterologist and co-inventor of the Cologuard system.
The test was 92 percent accurate at identifying patients with colon cancer and 69 percent accurate at identifying patients with the kinds of bowel lesions or polyps that indicate a high risk for cancer, according to clinical trial results published Wednesday in the New England Journal of Medicine.
“Time will tell,” Ahlquist said. “It’s our hope that many individuals who are not being screened because of their reticence to undergo colonoscopy will choose to undergo screening with a noninvasive option like this.”
Regular screening for colon cancer is recommended at age 50 — earlier for people with family histories or greater risks — and was credited in a report Monday by the American Cancer Society for a decline over the past decade in the U.S. rate of colon cancer mortality.
But the lack of uptake is also why colon cancer remains the third-leading cause of cancer mortality, and contributes to 50,000 deaths in the nation each year.
The DNA test comes with its own “eww” factor, in that people would need to fish out their own stool samples and package them to send in for testing.
But market research by the test kit manufacturer, Exact Sciences of Madison, Wis., indicates that people aren’t bothered as long as the test is effective and covered by health insurance. Surveys showed only 3 percent of people being put off by having to collect a stool sample.
“Our kit comes in its own sturdy box … and the patient also uses it to return the sample to the lab,” said Exact Sciences spokeswoman Cara Tucker. Test results would be sent to doctors in about two weeks.
The findings come from a company-funded clinical trial of 10,023 people who were at normal risk for colon cancer. They come about two weeks before a U.S. Food and Drug Administration committee is scheduled to decide whether the test is safe and effective for clinical use. In an unusual step, the U.S. Centers for Medicare and Medicaid Services are reviewing the test before the FDA review is complete — an indication that the federal agency might expedite Medicare coverage of the test for the nation’s elderly population.
Federal approval could mean the Cologuard test would be available as early as midsummer.
Compares to existing test
The study was a head-to-head comparison with an existing test called FIT, which detects cancer by finding hidden blood in stools, and showed that the new DNA screening found more cancers and cancer risks.
Cologuard works because tumors and polyps in the colon “shed” cells that are detectable in human waste, Ahlquist explained. However, the DNA test resulted in some false positives — about one in 10 tests suggested patients had colon cancer or an imminent risk for it, when they didn’t.
In clinical care, patients with positive results from Cologuard would undergo colonoscopies to confirm the results, said Dr. Thomas Imperiale, an Indiana gastroenterologist who was lead author of the study.
False positives do cause stress and anxiety, he said, but in the end they would direct patients to receive colonoscopies that they would have likely received anyway if the DNA test didn’t exist.
The rate of false negatives was low, and would likely be overcome if patients repeated the test over time, he said. Whether the test would be recommended annually, or less frequently, is unclear. The cost remains unclear as well, though it would presumably be cheaper than a colonoscopy, which requires a visit to a specialty clinic or hospital.
Dr. Cathleen Clouse, a HealthEast family practice doctor in Maplewood, said she would welcome a new alternative for the many patients who are uneasy about colonoscopies or dislike the voluminous fluids they must consume in advance to clean out their bowels.
Two of her patients were referred to specialty clinics for colonoscopies and suffered the rare complication of having their bowels perforated.
“Given the alternative, I think people are going to choose the DNA test,” she said. “You’d be surprised what people are willing to do because they don’t want the colonoscopy.”
Jeremy Olson • 612-673-7744
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