A blood test can pick up cancers up to four years before symptoms appear, researchers say, in the latest study to raise hopes of early detection.
A team led by researchers in China say the non-invasive blood test – called PanSeer – detects cancer in 95% of individuals who have no symptoms but later receive a diagnosis.
“We demonstrated that five types of cancer can be detected through a DNA methylation-based blood test up to four years before conventional diagnosis,” the team wrote in the journal Nature Communications.
They said the test was unlikely to be predicting cancer but rather picking up on cancerous growths that had not yet caused symptoms or been spotted by other methods.
Such tests, known as liquid biopsies, have become the focus of much research as they offer a non-invasive way to screen patients..
The new study is not the first to report positive results for a blood test for early detection of cancer. However, the team said the research was exciting because it showed cancers could be detected before patients showed any indication of symptoms – something few studies have shown before.
The researchers reported how the new test was based on screening particular regions of DNA found in blood plasma for telltale tags, called methyl groups, that often crop up in tumour DNA. The team said they used techniques that allowed them to pick up even very small levels of such DNA.
They then used machine learning algorithms – a type of artificial intelligence – to develop a system that could determine whether any DNA found circulating in the blood was indeed shed by tumours, based on the presence of these methyl groups.
To develop the test, the team used blood plasma samples collected from individuals in China between 2007 and 2014 as part of a wider research endeavour.
Overall, 414 samples were used from participants who remained cancer-free at least five years after the blood was taken, and 191 samples were used from participants who were diagnosed with stomach, colorectal, liver, lung or oesophageal cancer within four years of the blood being collected. The team also used samples from biobanks from 223 patients already diagnosed with one of the five cancers.
After training the system on about half of the samples, the team tested their approach on the remainder.
The results revealed PanSeer flagged cancer in 88% of participants who had already been diagnosed and in 95% of participants who were not diagnosed with cancer but later went on to develop the disease. The test correctly identified those without cancer 96% of the time.
The study has limitations, including that it is based on a relatively small number of samples, storage was not optimal, and the team has raised some concerns about possible contamination. Also, the test cannot identify which type of cancer an individual has.
But Dr Eric Klein, of Cleveland Clinic’s Taussig Cancer Institute, who was part of a team that previously revealed a liquid biopsy that can identify 10 different types of cancer at an early stage and predict which organ is affected, welcomed the new research.
“This is an exciting study which provides further confirmation that methylation-based assays can detect cell-free circulating tumour DNA and may form the basis for new screening tests that detect cancer at early stages,” he said. “There is a need for such tests to screen for cancers for which there are currently are no effective screening paradigms.”
Samantha Harrison, a senior early diagnosis manager at Cancer Research UK, said: “The PanSeer test has achieved encouraging initial results. Promisingly, the test may be able to detect cancer in blood samples taken years before diagnosis. But these are early results that now need to be validated in larger studies.”
