A blood test developed and checked using blood samples from 4000 people can accurately detect more than 50 cancer types, often before any symptoms appear. It was most accurate at identifying 12 especially dangerous types, including pancreatic cancers that are usually diagnosed only at a very late stage.
Many groups around the world are trying to develop blood tests for cancer, often referred to as “liquid biopsies”. Michael Seiden at US Oncology, a company involved in cancer care, and his team explored several ways of testing for cancer based on sequencing the DNA that dying cells release into the bloodstream.
The team found that looking at methylation patterns at around a million sites was the most promising. Methyl groups are chemical tags added to inactive genes by cells, and cancer cells have abnormal methylation patterns.
Next, the team trained a machine learning system on blood samples from 1500 people with untreated cancer and 1500 with no cancer diagnoses. They then used the system to analyse 650 blood samples from people with cancer and 610 without.
The machine learning system had a specificity of 99.3 per cent, meaning 0.7 per cent of people were wrongly identified as having cancer when they did not. “Specificity is extremely important because you don’t want to raise false alarm in people who are well,” says Seiden.
The true positive rate – the proportion of cancers detected – varied depending on how advanced the cancers were. For the 12 most deadly cancers, the true positive rate was 39 per cent in stage I, 69 per cent in stage II, 83 per cent in stage III and 92 per cent in stage IV. For all types, the corresponding rates were 18 per cent, 43 per cent, 81 per cent and 93 per cent.
The test is now being trialled in a larger group of people.
“This is a landmark study and a first step toward the development of easy-to-perform screening tools,” the editor of the journal that published the paper, Fabrice André at the Institut Gustave Roussy in France, said in a statement. “Earlier detection of more than 50 per cent of cancers could save millions of lives every year worldwide.”
Journal reference: Annals of Oncology, DOI: 10.1016/j.annonc.2020.02.011
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