Highly Accurate At-Home Colon Cancer Test Approved
DNA analysis of stool boosts accuracy rate of Cologuard to more than 90 percent, researchers say
To assess the potential of the DNA method, nearly 10,000 men and women aged 50 and older were screened for colon cancer and precancerous polyps at one of 90 sites across the United States and Canada. All were considered at average risk for colon cancer.
Each patient was screened three ways: by means of a standard colonoscopy; a commercially available fecal test (FIT); and the new DNA test, which requires patients to collect their own stool sample at home and mail it in for laboratory analysis.
In the end, colonoscopy screenings -- considered the gold standard of colon cancer screening -- revealed colon cancer in 65 participants, while another 757 were found to have advanced precancerous lesions.
The new DNA test accurately detected 60 of those 65 cancers. The FIT test spotted only 48 cancers, with an accuracy rate of 74 percent compared to 92 percent for the new test.
The DNA test was less accurate with respect to precancerous lesions, spotting about 42 percent of cases. Yet that still topped FIT, which detected roughly 24 percent of precancerous lesions. Cologuard's sensitivity was 69 percent for precancerous polyps most likely to progress to cancer versus 46 percent for the FIT test.
However, the DNA test was more likely to falsely suggest the presence of cancer than either a colonoscopy or FIT testing.
"It [the DNA test] is not a perfect test," Itzkowitz acknowledged. "But neither is a colonoscopy. Also, I don't think we're saying that this test should be done as a replacement for a colonoscopy, but rather as an adjunct. Certainly if a person who does this test comes out with a positive reading then they will need to do a colonoscopy afterwards to confirm it."
Dr. Frank Sinicrope, a professor of medicine and oncology at the Mayo Clinic in Rochester, Minn., said, "These data demonstrate the superiority of stool DNA testing compared to FIT for colorectal cancer screening."
Sinicrope, who was not part of the study team, also suggested that the Cologuard method might offer some advantages over standard colonoscopies.
In particular, he pointed to the DNA test's success in identifying certain advanced-stage polyps, noting such precancerous growths are typically flat and "located in the right side of the colon and are difficult to detect at colonoscopy."
Nevertheless, Sinicrope said there are still "important issues that await further research." Those would include determining how best to deal with false positive results and establishing how often patients should take the DNA test to maximize its screening potential.