A team of researchers has developed the first blood test that can detect with a high degree of accuracy more than 50 types of cancer and identify in which tissue the cancer had its origin. Detection is often before there are any clinical signs or symptoms of cancer and may be particularly useful in cancers that are usually hard to detect. The team hopes that it will eventually be suitable for mass population screening.
The research published in the journal Annals of Oncology, showed that the test had a 0.7% false positive, which means that less than 1% of people who take the test will be wrongly told they have cancer. This the researchers note, compares very favourably with the current US screening programme for breast cancer, where false positives can be at 10%.
The test detects the small amount of DNA that is shed by tumours into the blood. This DNA is chemically different from DNA shed from healthy tissue and this difference can be detected by the test. The chemical difference – known as methylation – has a distinct pattern to it depending on the type of tumour and its origin. The test – a machine learning classifier (an algorithm) – has been set up to compare the pattern of methylation in the DNA to a database of millions of methylation patterns found on DNA present in the blood of patients with and without cancer.
The system was trained to detect which methylation patterns were linked to which type of cancer. The more advanced the disease was the better the detection, with the cancer detected correctly in 93% of those with stage IV cancer. The team are particularly excited about the use of the system to detect certain cancers that are usually very difficult to detect, such as pancreatic cancer. The system correctly identified 63% of those with stage I pancreatic cancer, rising to 100% in stage IV.
The team also found that the system could shed light on the type or origin of the cancer. For 96% of samples deemed to show cancer, the test was able to offer a prediction for the tissue origin of the cancer, with 93% of these predictions found to be correct.
The study is funded by GRAIL, the maker of the blood test. Researchers are continuing to validate the test in large, prospective studies in the USA (STRIVE and PATHFINDER studies) and the UK (SUMMIT study), and to examine its feasibility for screening populations.
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