'Our findings indicate that the output from genetic testing can differ markedly depending on which test is applied,' the researchers wrote in JAMA Oncology. This can lead to different treatment recommendations, depending on which test was used.
The research was led by Professor Anthony Blau of the University of Washington and Dr Sibel Blau, a clinical oncologist. Patients were given two simultaneous tests – traditional tissue biopsy and novel liquid biopsy.
The researchers compared two liquid biopsies – FoundationOne and Guardant360. FoundationOne tests tumour tissue for 343 genes. Guardant360 tests blood to examine 70 genes in the cell-free circulating tumour DNA (cfDNA). Each test costs around $5800.
'With a tumor biopsy, it's like you read the book cover to cover. With a liquid biopsy, you read an entire shelf of books, but you only read the dust jackets,' Dr Justin Odegaard, the senior medical director of Guardant Health, told The Atlantic.
The tests identified 45 mutations in total within the patient group. But only 10 mutations (22 percent) were discovered by both platforms. This meant that the tests gave different drug recommendations to the majority of patients.
The new study only tested nine patients, but the findings match other work. A paper from researchers at Northwestern looking at liquid versus tissue biopsies reported that over half of the mutations found by one test did not show up in the other.
Which test is more accurate? 'There is no easy answer,' Dr Richard Schilsky, the chief medical officer of the American Society of Clinical Oncology, told The Atlantic. 'Because nobody actually knows what is the truth in terms of what's happening inside a person's tumor throughout the body.'
Dr Sibel Blau added that she thinks liquid biopsies 'are not really ready for primetime' and that clinicians should rely on tissue biopsy results until there is more research on the effectiveness of liquid biopsies.