Numerous types of cancer could be screened with a high degree of accuracy from a single blood test that is now being developed.
The test, developed by Grail, a healthcare company focused on early detection of cancer, uses next-generation sequencing technology to probe DNA for tiny chemical tags (methylation) that influence whether genes are active or inactive.
Researchers at the Dana-Farber Cancer Institute in the US found that when applied to nearly 3,600 blood samples — some from patients with cancer, some from people who had not been diagnosed with cancer at the time of the blood draw — the test was able to successfully pick up a cancer signal from the cancer patient samples, and correctly identify the tissue from where the cancer began (the tissue of origin).
The new test looks for DNA, which cancer cells shed into the bloodstream when they die. In contrast to ‘liquid biopsies’, which detect genetic mutations or other cancer-related alterations in DNA, the new technology focuses on modifications to DNA known as methyl groups. Methyl groups are chemical units that can be attached to DNA, in a process called methylation, to control which genes are turned ‘on’ and which are ‘off’. Abnormal patterns of methylation turn out to be, in many cases, more indicative of cancer, and cancer type, than mutations are. The new test zeroes in on portions of the genome where abnormal methylation patterns are found in cancer cells.
“Methylation-based assays outperform traditional DNA-sequencing approaches to detecting multiple forms of cancer in blood samples,” said one researcher. In the study, investigators analyzed cell-free DNA (DNA that had once been confined to cells but had entered the bloodstream upon the cells’ death) in 3,583 blood samples, including 1,530 from patients diagnosed with cancer and 2,053 from people without cancer. The patient samples comprised more than 20 types of cancer.
The overall specificity was 99.4 percent, meaning only 0.6 percent of the results incorrectly indicated that cancer was present. For the 97 percent of samples that returned a tissue of origin result, the test correctly identified the organ or tissue of origin in 89 percent of cases. Detecting even a modest percent of common cancers early could translate into many patients who may be able to receive more effective treatment if the test were in wide use.
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