The use of a blood test to detect more than 50 types of cancer has sparked more debate after findings from two different studies of its use.
Results from a study in 25,000 adults from the US and Canada over a year reported nearly one in 100 people getting a positive result from the Galleri test, with cancer later confirmed in 62% of cases.
Presenting the results at the European Society of Medical Oncology, the researchers from Oregon Health and Science University in Portland, US, said the data showed that the test could ‘fundamentally change’ the approach to cancer screening.
They also reported that the test correctly ruled out cancer in over 99% of those who tested negative.
The data from the PATHFINDER II trial has not yet been published in a journal, but the researchers told delegates that when combined with breast, bowel, lung and cervical screening the number of cancers detected overall increased seven-fold.
Crucially, three-quarters of the cancers detected, such as ovarian, liver, stomach, bladder and pancreatic cancers, currently have no screening programme, they added.
Need for proactive follow-up
A second study of the test presented at the Early Detection of Cancer Conference in Oregon by the University of Oxford, found that when used in 6,000 patients presenting to their GP with symptoms in England and Wales the positive predictive value was 84.2%.
This is an improvement on previously reported results in the same study of 75.5% because, when followed for two years, more patients ended up being diagnosed with cancer.
Study lead Dr Brian Nicholson, associate professor in the Nuffield Department of Primary Care Health Sciences at the University of Oxford, said the conversion of false positive results to cancer diagnosis in longer follow-up of the SYMPLIFY study showed the importance of proactive follow-up.
‘One third of the apparent false positive results were actually cancers the standard-of-care diagnostic process couldn’t immediately identify,’ he said.
There is also a three-year trial involving 140,000 NHS patients in England, expected to be published next year, which will inform wider use of the test.
‘Currently unsuitable for population screening’
Speaking on the results from the US trial using the test as a screening tool in the over 50s, UK experts had mixed reactions.
Professor Nitzan Rosenfeld, director of the Barts Cancer Institute in London, said the results were ‘impressive’ and the 62% figure was ‘provides strong evidence that this test could be safe and informative’.
He said: ‘Importantly, more than 50% of the cancers detected by the Galleri test in this study were early stage (stages 1-2), and more than 75% of them do not have common screening options.’
But he cautioned, along with others, that more research was needed looking at the impact on mortality.
Professor Anna Schuh, professor of molecular diagnostics, and honorary consultant haematologist at the University of Oxford, said the data so far suggested the test had not performed as well as expected.
‘133 cancers were detected by the test, so only roughly about a third of what the test should be expected to detect,’ she said. ‘To achieve this, over 23,000 people had to be screened.’
She noted it was a large, important study but that the ‘low pick-up rate in this specific cohort combined with the cost of the assay in my view makes this approach currently unsuitable for population screening based on this current data’.
A version of this article was originally published by our sister publication Pulse.