New blood test detects cancer four years before conventional diagnosis

It is no secret that early detection of cancer influences treatment options and survival rates.
 
But the ability to detect cancer long before it is symptomatic is preferable to picking up the disease once it has progressed.
 
Now, new research published in Nature Communications describes PanSeer, a non-invasive blood-based cancer-screening test based on circulating tumour DNA (ctDNA) methylation. The study found that PanSeer could detect cancer four years before current standards of care.
 
For the research, PanSeer was performed on plasma samples from healthy subjects in the Taizhou Longitudinal Study (TZL). The cancers detected included stomach, oesophagus, colorectum, lung and liver.
 
The authors reported PanSeer detected those cancers in 88% of post-diagnosis patients, with a specificity of 96%. They also found that PanSeer detected cancer in 95% of asymptomatic individuals who were later diagnosed, though they say future longitudinal studies are required to confirm this result.
 
Professor Peter Gibbs is the Joint Division Head of Personalised Oncology at the Walter and Eliza Hall Institute of Medical Research.
 
He told newsGP this research adds further weight to growing evidence on the use of screening blood tests to detect cancer.
 
‘It’s supporting a very interesting and exciting area of cancer research,’ he said.
 
Professor Gibbs says there have been ‘many other groups’ of researchers working on similar research, and that he himself has been part of this process.
 
‘Some of that research is more advanced, where they’ve done prospective studies,’ he said.
 
But he believes this research helps validate this technology. Professor Gibbs says the ‘most novel’ aspect of these findings relates to the time between the blood test and the cancer diagnosis.
 
‘That was one of the lead aspects of the study, that the study detected the cancers up to four years before the cancer was diagnosed,’ he said.
 
‘And as we understand it, early diagnosis is important and the more time before the patient is symptomatic that you can diagnose the cancer, the better the outcome.’
 
However, Professor Gibbs is concerned about a number of weaknesses in this research.
 
One of those concerns is that the researchers found people with cancer, and then retrospectively looked back at their blood samples.
 
‘That is not quite the same as looking at [a patient’s] blood and then trying to work out who has got cancer and who hasn’t,’ he said.
 
Another issue lies in determining what type of cancer a person has.
 
‘So the challenge can be, for example, if you find mutated DNA in the blood of someone who looks otherwise healthy, how do you find the cancer that the person has?’ Professor Gibbs said.
 
‘That’s not a trivial exercise.’
 
Professor Gibbs is also concerned about the high rate of false positives.
 
‘About 5% of the normal patients that didn’t get cancer also had a positive test, so their false positivity rate was actually quite high compared to other series, where it’s typically under 1%,’ he said.
 
‘That sort of ratio, of 5:1, is way too high.
 
‘You really want to be able to find the ones with cancer, but you don’t want to be finding lots of people who don’t have cancer and then cause a lot of trauma unnecessarily, and [have patients undergo] expensive and potentially dangerous investigations.’
 
At this stage, Professor Gibbs says more research into this field is needed.
 
However, he expects that cancer-detecting blood tests will soon be a topic about which patients will approach their GP.
 
‘I think there’s going to be a lot of direct-to-patient marketing in the not-too-distant future,’ he said.
 
‘Patients will start asking their GP, “Should I have this blood test done?”’
 
The question is only hypothetical for now, as the technology is not available to the public. But even when it does become available, Professor Gibbs says it is important for clinicians to understand the risks and benefits associated with such tests.
 
‘We don’t know what the real benefit is to patients, particularly what the downside will be, and how the two balance up,’ he said.
 
‘The real question is, how accurate are those tests? And what are the interventions [a doctor can do after receiving the result] that can make a difference?’
 
Professor Gibbs says this technology is still firmly ‘in the research domain’ and that it is at least five-plus years before a clinically actionable cancer-detecting blood test is developed.
 
But he believes it will happen and, when it does, it will hopefully change the landscape of cancer diagnosis.
 
‘It’s showing very promising results that it can diagnose cancer early,’ he said.
 
‘And it probably will make a difference to patient care.’
 
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