Results of a promising trial in people with brain tumours suggests that a specific blood test could be used for more accurate diagnosis, without the need for invasive procedures.

The blood test based on circulating-tumour DNA (ctDNA) has been found to accurately classify different types of brain tumours and could allow for better treatment planning for patients in the future.

Currently getting a definitive brain tumour diagnosis relies on obtaining a sample of tissue through invasive surgery. It’s also difficult to classify a brain tumour and find out its grade, information that helps doctors and patients to plan treatment. This is because under a microscope low grade brain tumours can look very similar to more aggressive ones, making grading a brain tumour very challenging.

A better and more reliable way to diagnose and classify brain tumours without the need for a tissue sample or surgery could “transform patient care”, says Dr Gelareh Zadeh at the Princess Margaret Cancer Centre in Toronto. “It would have a tremendous impact on how we treat these cancers, and in how we plan our treatments,” she adds.

Dr Zadeh and her colleagues, including Dr Daniel Carvalho, have previously developed a blood test called a liquid biopsy that looks at hundreds of thousands of alterations in fragments of DNA molecules circulating in the blood (ctDNA). They used the results of this analysis to develop a test to detect and classify multiple kinds of solid tumours.

Next, the team compared tumour samples taken from patients with brain cancer with the results of their analysis of ctDNA in blood samples from 221 patients.

Using this approach, they matched the ctDNA to the tumour DNA. They then developed a computer program to classify the brain tumour type based solely on the ctDNA.

Prior to this, it was thought the impermeable barrier between the blood and the brain made it impossible to detect any brain cancers with a blood test, says Dr Zadeh. “But because this test is so sensitive in picking up even small amounts of highly specific tumour-derived signals in the blood, we now have a new, non-invasive way of detecting and discriminating between common brain tumours – something which was long thought impossible,” says Dr Zadeh.

The research was presented at American Association for Cancer Research 2020 annual meeting, and published in the journal Nature Medicine[1]. In the same journal, Dr Carvalho and colleagues at the Dana-Farber Cancer Institute at Harvard University published a paper that found the same blood test can accurately identify kidney cancer from ctDNA obtained from blood plasma or urine samples[1].

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[1] Nuzzo, P.V., Berchuck, J.E., Korthauer, K. et al. Detection of renal cell carcinoma using plasma and urine cell-free DNA methylomes. Nat Med 26, 1041–1043 (2020). https://doi.org/10.1038/s41591-020-0933-1