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New colorectal screening test effectively measured precancers
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A new colorectal screening test that measures DNA methylation had a sensitivity of 64% in detecting precancers, according to findings.
David Ahlquist, MD, professor of medicine and a consultant in gastroenterology at the Mayo Clinic in Rochester, Minn., presented the results during a press conference.
“Right out of the block, this exceeded our expectations,” Ahlquist said. “Not another assay comes close to this sensitivity.”
The product is under development by Exact Sciences, a molecular diagnostics company based in Madison, Wis., in conjunction with Ahlquist and the Mayo Clinic. The novel assay can capture direct sequences of target genes using quantitative allele-specific real-time target and signal amplification.
The study involved an evaluation of 456 samples from Exact Sciences laboratories, which Ahlquist referred to as the training set, and 222 samples from the Mayo Clinic, which were called the test set. Samples were taken from sites in Denmark and Toronto, and labs at Johns Hopkins Hospital and the Mayo Clinic.
“The assay detected precancers in both the training set and the test set equally, at 64% in both groups,” Ahlquist said. “We wanted to target curable stage cancers, and that is where the test is most effective.”
He said the assay had an 85% sensitivity overall for cancer detection; the breakdown was 89% in the training set and 78% in the test set. The difference between the two sets was not significant, according to Ahlquist.
The sensitivity was 84% for stage I cancers, 80% for stage II, 95% for stage III, 87% for stages I, II and III combined and 69% for stage IV cancers.
“As adenomas grow toward cancer, the test becomes increasingly more sensitive,” he said. “For adenomas greater than 3 cm, the sensitivity becomes 91%.”
According to Ahlquist, the assay has the capacity to detect cancers on both sides of the colon. “Cancers on the far side of the colon were also detected,” he said. “Detection was not affected by lesion site. This is an important step forward.”
The overall results of the study are encouraging, Ahlquist said, adding that the results are strong enough to move forward to the next step, which will be to refine the test and begin prospective studies across multiple centers.
“The big idea in screening is to detect the precursors,” he said. “If you do not detect precursor lesions, you will not prevent the cancer. If you can detect it early enough, you can prevent mortality.”