A blood test designed to enable simple screening for colon cancer has been hailed by experts as a major advance. The test detects cancer due to a chemical change called methylation that occurs disproportionately in two key genes in colorectal tumor cells.
Since more people should be willing to have a simple blood test, the screening method could help identify those patients who need a more invasive, more diagnostically rigorous colonoscopy.
The U.S. death toll from the condition is around 50,000 a year. The American Cancer Society recommends that men over the age of 50 have about one colonoscopy every 10 years, and that those at a higher risk be screened earlier and more often. Yet until now, only invasive colonoscopies and stool tests have been available and compliance by those deemed in need of screening is disappointingly low, at less than 50 percent. Screening programs have been shown to cut deaths by allowing more victims to receive earlier, curative treatment so a simpler test could save lives by encouraging more people to get screened.
The developers of the new test, OncoMethylome Sciences, based in Liège, Belgium, say their method, which relies on one three-milliliter sample of blood, has the potential to boost compliance rates and conserve precious health service resources.
The test identifies the presence of methylated SYNE1 and FOXE1 genes, which mark out colorectal cancer cells. The researchers compared test results from 686 healthy control patients with 193 patients already diagnosed with the disease. The test was able to detect colorectal cancer in 77 percent of those subjects with the disease, according to data presented at the Congress of the European Cancer Organization in Berlin, Germany, on Monday. It correctly identified healthy, noncancerous patients in 91 percent of cases.
“This test has potential to provide a better balance of performance, cost-effectiveness, and patient compliance than other options currently available for colorectal cancer screening,” says Joost Louwagie, vice president of product development at OncoMethylome.
Louwagie hopes that with further testing and refinements the test will become more sensitive and provide fewer false-positive results. But he says that even a 77 percent sensitivity would be “very useful” if it were applied to the large numbers of people who decide not to have screening using more-intrusive methods. He stresses, however, that colonoscopies remain the gold standard for diagnosing the disease.
Ernst Kuipers, head of the colorectal screening program and a professor of medicine at Erasmus University Medical Center in Rotterdam, praises the results. “This is an excellent new method, technically very well done,” he says. “It represents a major advance on what we have now.”
Kuipers says the 77 percent accuracy in detecting cancer-containing samples is “a good result.” In comparison, the fecal-immunological screening method that he has been researching is around 60 percent accurate. He notes, however, that the specificity of the blood test–its ability to correctly identify healthy patients–will need to improve. “In practice, everyone over 55 would be screened, perhaps every two years,” he says. “That’s millions of people. So, if you had more than 5 percent false-positive rates, the number of follow-up colonoscopies you’d need to do would become too great.”
Kuipers says that the specificity of the test needs to be at least 95 percent for it to be used in colorectal screening and that a large-scale evaluation will be vital.
With this in mind, Louwagie and colleagues are enrolling people in a prospective colorectal screening study at several German colonoscopy centers. “We plan to complete enrollment of 7,000 people by the end of 2009,” he says.
The trials should also shed more light on how effective the test is at detecting the very earliest stages of colorectal cancer. Such a gene test will not be able to spot precancerous polyps. But it could be particularly effective if it can detect stage-one and stage-two colorectal cancers, which are almost always curable with surgery.
A new paper by Kuipers, due to appear in Journal of the National Cancer Institute, will provide new evidence that colorectal screening can ultimately save health services money, he says. But he believes that the most important measure will be a reduction in the number of colon cancer deaths. Kuipers notes that older, repeat-stool type testing, which was considered ineffective and not very sensitive, has been shown to have cut colorectal cancer deaths by 15 percent. He says that a reasonably sensitive and simple test with higher compliance levels could prevent many more colon cancer deaths.
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