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False positive Cologuard test not linked to higher rates of death, cancer
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Patients who have a false positive Cologuard test result followed by a negative colonoscopy did not have higher rates of subsequent cancer or death compared with true negative patients, according to results from the LONG-HAUL cohort study.
These findings led investigators to conclude that false positive patients do not require aggressive follow-up evaluation.
Patients at average risk for colorectal cancer with a positive Cologuard (multi-target stool DNA [MT-sDNA] test; Exact Sciences) result require a follow-up diagnostic colonoscopy.
John B. Kisiel
“In screening-setting clinical studies, about 7-13% of patients had a positive MT-sDNA but a negative follow-up colonoscopy,” John B. Kisiel, MD, of the division of gastroenterology and hepatology at the Mayo Clinic in Rochester, Minn., told Healio Gastroenterology. “Patients in this situation are concerned that the colonoscopy may have missed a colorectal cancer or pre-cancer and providers are concerned that these patients may need subsequent diagnostic studies to look for cancers in the upper part of the gastrointestinal tract that could shed abnormal DNA into stool. We wanted to know if patients with a false positive MT-sDNA test were at increased risk of long-term adverse health events, such as subsequent cancer diagnoses or even death.”
Kisiel and colleagues retrospectively evaluated 1,050 participants from previous studies of the MT-sDNA test or a prototype version from before the test was approved in August 2014 (median age, 65.6 years; 54% women). Using a national database, they contacted and interviewed most patients or their relatives, and followed others forward through their medical records (median follow-up, 4 years).
Overall, six patients were lost to follow-up, and eight aerodigestive (lung or gastrointestinal) cancers occurred.
“This rate was similar to what would be expected in the general U.S. population,” Kisiel said.
The investigators found no differences in the rates of death or subsequent cancer diagnoses of all types between false positive patients and true negative patients whose stool test and colonoscopy were both negative.
When looking only at the aerodigestive cancers, among participants in each study there were no differences between false positive and true negative test groups.
When calibrating the results to pool rates across all three prototype tests, the rate of aerodigestive cancers appeared to be higher among the false positive patients than true negative ones, but still did not exceed the rate expected in the general population.
Additionally, none of the subsequent aerodigestive cancers in false positive patients occurred within 3 years of the stool test.
“Because cancers of the gastrointestinal tract tend to be aggressive and grow rapidly, this long delay in presentation makes it very unlikely that additional diagnostic testing at the time of colorectal cancer screening would have found them, i.e. they were probably not present at the time of the false positive stool test,” Kisiel said. “Based on this information, it appears that asymptomatic patients with a false positive MT-sDNA tests after a high-quality colonoscopy do not need to undergo additional work-up for other cancers. Further work will be needed to confirm these findings.” – by Adam Leitenberger
Disclosures: Kisiel and several other researchers report Mayo Clinic has an intellectual property agreement with Exact Sciences under which they, as inventors, may receive royalties.
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