A blood test could pick up on more than 50 types of cancer before symptoms strike, research suggests.
In the test's third and final study, scientists from the Cleveland Clinic in Ohio analysed the blood samples of more than 2,800 cancer patients and over 1,200 people without the disease.
The test correctly identified the cancer patients just over half (51%) of the time, whose tumours ranged from small grade one to advanced grade four.
It also picked up on the healthy volunteers with 99.5% accuracy, giving the test a false positive rate of just 0.5%.
The test even flagged where in the body a patient's tumour was located in nearly nine in 10 (88%) cases.
Developed by the healthcare company Grail, the test is already available on prescription in the US to complement existing screening programmes, like mammograms and smears.
The Cleveland scientists believe it is accurate enough to be rolled out as a mass screening test for people who are at risk of cancer, like the elderly, but have not developed symptoms.
Grail has also partnered with the NHS to investigate the test's potential in a study of 165,000 Britons, starting later in 2021.
One in two people born after 1960 in the UK will statistically develop cancer at some point in their life.
The NHS routinely screens for cancers of the cervix, breast and bowel. In the US, medics also look for tumours of the lung and prostate.
Spotting any cancer before stage four could reduce tumour-related deaths in the US by
15% within five years, the Cleveland scientists wrote in the journal Annals of Oncology.
"Finding cancer early, when treatment is more likely to be successful, is one of the most significant opportunities we have to reduce the burden of cancer," said study author Dr Eric Klien.
"These data suggest – if used alongside existing screening tests – the multi-cancer detection test could have a profound impact on how cancer is detected and, ultimately, on public health."
Grail's test analyses a sample of blood for so-called cell-free DNA (cfDNA), which tumours shed.
The cfDNA is then checked for methylation – when so-called methyl groups are added to the genetic material, changing its function.
Based on these results, artificial intelligence works to detect any abnormal methylation that may suggest cancer, with a verdict available within 10 working days of the sample arriving at the laboratory.
In the third Circulating Cell-free Genome Atlas (CCGA) study, the test's accuracy on picking up on all the 50 plus cancers – stages one to four – came in at 51%.
This rose to 67% for 12 specific tumours at stages one to three, with these accounting for two thirds of all cancer deaths in the US every year – including those affecting the pancreas, bowel and oesophagus.
The test was better able to pick up on the cancer patients with advanced disease, 16% at stage one versus 90% at stage four, when a patient is more likely to have symptoms.
Accuracy also varied according to the type of the cancer.
For tumours without a mass screening programme – like those affecting the pancreas, liver and oesophagus – the accuracy was double that of the cancers that are routinely screened for – such as those affecting the breast, bowel and cervix.
The test's ability to pick up on blood cancers, lymphoma and myeloma, came in at 55%.
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"We believe cancers that shed more cfDNA into the bloodstream are detected more easily," said Dr Klein.
"These cancers are also more likely to be lethal and prior research shows this multi-cancer early detection test more strongly detects these cancer types.
"Cancers such as prostate shed less DNA than other tumours, which is why existing screening tests are still important for these cancers."
Across all three CCGA studies, the test has assessed the blood of more than 15,000 people.
"Early detection of cancer is the next frontier in cancer research as it could save millions of lives worldwide," said Professor Fabrice André, editor in chief of Annals of Oncology.
"Developing technologies that address this issue is the first step. Next steps will include the development of new therapeutic interventions.
"In parallel, major efforts related to population awareness must continue or all these efforts will not lead to transformation of outcomes."
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