Highly Accurate At-Home Colon Cancer Test Approved
DNA analysis of stool boosts accuracy rate of Cologuard to more than 90 percent, researchers say
Commonly used stool tests such as FIT (fecal immunochemical testing) rely on detecting blood in the stool. The new Cologuard test checks for blood as well as abnormal DNA, "with the advantage that some lesions, even cancers, don't bleed very much," Itzkowitz explained.
But the Cologuard test also features a DNA analysis not included in other fecal exams.
"By increasing the pick-up rate in this way," said Itzkowitz, "we found that the new test had a 92 percent sensitivity for detection of colorectal cancer. That kind of result is really unprecedented for a noninvasive stool-based screening."
The research was funded by Exact Sciences Corp., which is based in Madison, Wisc.
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."