Blood test to detect multiple types of cancer
US researchers are developing a blood test that has shown the ability to screen for numerous types of cancer with a high degree of accuracy, with the results presented at the European Society for Medical Oncology (ESMO) 2019 Congress in Barcelona.
The test, developed by California biotech company GRAIL, 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 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 ‘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 test zeroes in on portions of the genome where abnormal methylation patterns are found in cancer cells.
The study saw investigators analyse cell-free DNA (DNA that had once been confined to cells but had entered the bloodstream upon the cells’ death) in 3583 blood samples, including 1530 from patients diagnosed with cancer and 2053 from people without cancer. The patient samples comprised more than 20 types of cancer, including hormone receptor-negative breast, colorectal, oesophageal, gallbladder, gastric, head and neck, lung, lymphoid leukaemia, multiple myeloma, ovarian and pancreatic cancer.
The test successfully picked up a cancer signal from the cancer patient samples, with an overall specificity of 99.4% meaning only 0.6% of the results incorrectly indicated that cancer was present. The sensitivity of the assay for detecting pre-specified high-mortality cancers (the percentage of blood samples from these patients that tested positive for cancer) was 76%. Within this group, the sensitivity was 32% for patients with stage I cancer; 76% for those with stage II; 85% for stage III; and 93% for stage IV. Sensitivity across all cancer types was 55%, with similar increases in detection by stage. For the 97% of samples that returned a tissue of origin result, the test correctly identified the organ or tissue of origin in 89% of cases.
“Our previous work indicated that methylation-based assays outperform traditional DNA-sequencing approaches to detecting multiple forms of cancer in blood samples,” said study lead author Dr Geoffrey Oxnard, from the Dana-Farber Cancer Institute.
“The results of the new study demonstrate that such assays are a feasible way of screening people for cancer,” he added, noting that detecting even a modest percentage 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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