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Cologuard is a noninvasive stool DNA test that detects red blood cells and certain DNA mutations that are associated with colon cancer. The test was approved by the U.S. Food and Drug Administration in 2014.
The new study included nearly 400 people at average risk for colon cancer, meaning they had no symptoms and no personal or family history of the disease or precancerous polyps. The patients had also not yet undergone more invasive screening procedures, such as colonoscopy.
At one year of follow-up, 51 of the patients (about 15 percent) had a positive result on the Cologuard test and were referred for colonoscopy, said a team led by Dr. Mark Prince of USMD Physician Services, a health system based in Dallas.
Of the 46 patients who received a follow-up colonoscopy, four were diagnosed with a colon cancer, 21 with advanced polyps (indicating a heightened risk for the cancer), and nine with non-advanced polyps.
The findings were to be presented Tuesday at the annual meeting of the American Academy for Cancer Research (AACR), in New Orleans. Research presented at meetings should be viewed as preliminary until published in a peer-reviewed journal.
"Colon cancer screening saves lives," Prince said in an AACR news release. "Colonoscopy is the best form of colon cancer screening, but for patients who will not have a colonoscopy, a noninvasive screening test like Cologuard is needed."
However, "despite the availability of various colon cancer screening options, more than 40 percent of Americans are not getting screened," he added. "This study highlights the opportunity to expand the screening population by offering new, patient-friendly methods."
Prince is also a speaker for Exact Sciences Corp., the Wisconsin-based maker of Cologuard.
"The study lacks a true evaluation of the benefit of this test as their patient selection is quite limited [46 patients]," said Dr. Jules Garbus, a colorectal surgeon at Winthrop-University Hospital in Mineola, N.Y.
Dr. David Bernstein is chief of hepatology at Northwell Health in Manhasset, N.Y. He pointed to the results of a recent study in the New England Journal of Medicine that found that the Cologuard test had only a 42 percent sensitivity -- meaning that it could only accurately spot a precancerous growth less than half of the time.
"The sensitivity of the test, in particular for precancerous polpys, is unacceptably low," Bernstein said, and "Cologuard should not be used as a substitute for colonoscopy when the better test, colonoscopy, is available."
Bernstein also reiterated that the study size of just 46 patients is too low to come to firm conclusions about Cologuard.
"In addition, not all colon cancers have the predetermined DNA mutations measured by Cologuard," Bernstein said, "meaning that other cancers may be missed by this test and we do not know the false-negative rate of Cologuard."
-- Robert Preidt
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