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The holy GRAIL blood test: a promise of early cancer diagnosis

6th October 2021 - 0 comments

With cancer as the second leading cause of death worldwide, GRAIL’s cancer detection test offers new hope to many. By using biomarkers in your blood, the Galleri test promises to catch cancer earlier, and in turn, save millions of lives.

Liquid biopsies – the analysis of tumours using biomarkers circulating in bodily fluids such as the blood – have received increasing attention over the past decade. They offer minimally invasive diagnostic tools that have the potential to detect, characterise and monitor cancers earlier than is possible with conventional methods.

One of the most well-developed methods involves detecting circulating tumour DNA (ctDNA). These fragments of DNA contain genetic defects representative of the tumour cells they originate from. Accordingly, identifying the presence of these genetic defects through techniques such as by DNA sequencing can help us diagnose cancer.

So, why is this not being done? Low amounts of ctDNA in blood, difficulties identifying suitable biomarkers, and high false-positive rates have so far been limiting the clinical value of liquid biopsies. However, recent progress in technology and plans for large scale trials is giving early cancer detection diagnostics new hope.

The holy GRAIL?

Since hitting the news back in November, a cancer detection blood test named Galleri – created by Californian company GRAIL, Inc. – has once again made the headlines. By coupling machine learning and DNA sequencing, the test looks for abnormal DNA methylation patterns indicative of cancer.

Having been met with a healthy dose of initial skepticism due to its potentially high false positive rate, the latest study illustrated impressively high levels of accuracy with an ability to detect more than 50 cancer types2.  

Across all cancer stages, specificity was 99.3%, indicating a low false-positive rate of 0.7%. This number is particularly important because false positives may lead to misdiagnosis, and costly follow-up procedures with significant emotional toll.

However, we still need to approach with caution. For example, for some cancer types the sample sizes were noted as particularly small by the authors. This prevents findings from being correctly extrapolated to real-world screening scenarios.

Additionally, while the ultimate goal is early diagnosis, the test is better at detecting cancer in individuals with advanced-stage cancer. Across all cancer types (>50) the test was able to accurately detect more than 80% of cancers but this figure drops below 25% for stage 1 cancers.

NHS roll out

Although we still await the final verdict on the GRAIL blood test, the next few years is set to provide us with some key information – with GRAIL undertaking a large-scale study in partnership with the NHS.

Enrolling 140,000 participants aged 50-79 with no symptoms and an additional 25,000 people with possible cancer symptoms, it is hoped that results from the study will be available by 20233. If outcomes are positive, the NHS plans to extend the availability of the test to 1 million more people across 2024 and 2025.

Future outlook

GRAIL recognise the limitations of their test, and have openly commented that it is not intended to replace established screening methods just yet – it simply supplements them. But, could liquid biopsies ever supersede invasive screening methods?

The jury’s still out on GRAIL’s blood test, but with biotechnology companies across the world seeking to further early-stage cancer detection – such as Ark and Ibex Medical analytics – it seems safe to say that cancer diagnostics is changing for the better. 

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References

1.      Cancer. https://www.who.int/health-topics/cancer

2.      Liu, M. C. et al. Sensitive and specific multi-cancer detection and localization using methylation signatures in cell-free DNA. Ann. Oncol. 31, 745–759 (2020).

3.      NHS England » NHS to pilot potentially revolutionary blood test that detects more than 50 cancers. https://www.england.nhs.uk/2020/11/nhs-to-pilot-potentially-revolutionary-blood-test/.

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