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Detecting cancer early with just one blood test.


The NHS is set to pilot a new blood test to improve its ability to detect cancer early.

Detecting cancer early with just one blood test.

The NHS is set to pilot a new blood test to improve its ability to detect cancer early. The Galleri blood test, developed by Californian healthcare company Grail, will be piloted with 165,000 patients starting in mid-2021.

Traditionally patients are referred to cancer services if they begin exhibiting concerning symptoms for cancer (such as weight loss, lethargy, blood in stools, urine or coughing), or if they qualify for the various screening programmes set up in the UK. Unfortunately, some cancers present with symptoms late, when cancer may already be too advanced, and screening programmes are only available for certain cancers that are prevalent, easy to test and easy to detect early. Currently, only half of all cancers in the UK are diagnosed at stage one or two, and the NHS aims to increase this number to 75% by 2028. The earlier cancer is found, the higher the likelihood of survival.

The Galleri blood test looks at methylated free DNA in the patient’s blood. Essentially this is DNA shed from cancer cells that exhibit markers and changes that are concerning for cancer mutation and uncontrolled tumour cell replication. GRAIL has been using AI to help interpret blood test results, and the findings appear to be promising. One of their studies showed the ability to detect over 50 types of cancer with a false positive rate of less than 1%.

The pilot programme will provide valuable data on the feasibility of using such tests to diagnose patients with cancer. Starting in 2021 it will be offered to 140,000 aged 50 to 79 with no symptoms, with further follow ups and blood tests over three years, and 25,000 patients with possible cancer symptoms who may have their diagnosis sped up with the blood test. If results are encouraging, over 1 million people may receive the test by 2025.

Such a test will be key in detecting cancers that have no effective screening options, or present with symptoms very late, and as a result have low survival rates. Lung, ovarian and pancreatic cancers would particularly benefit from this. Furthermore, this is just one blood test that can cover multiple different types of cancer, reducing the costs and complexity of running large scale screening programmes for patients.

Pancreatic cancer is a key example of this. It usually presents with painless jaundice, but this only happens when the cancer is large enough to block the ducts in the pancreas. At this stage, the cancer is usually so advanced little can be done beyond palliative treatment. If detected early, surgical options may finally be able to provide potentially curative treatment.

Whilst this is all positive news, we must take into account some limitations of the test. The test is still relatively new and is likely to pick up larger cancers (that, in turn, shed more DNA into the blood) earlier than smaller cancers. The touted 1?lse-positive rate for detecting 50 types of cancer also comes from a very small study with just 654 cancers, of which only 185 were in the early stages. In the early stages, the sensitivity (how easily it detects possible cancers) was less than 25%, and for stage 2 cancers it was less than 50%. If this was applied to the UK population, thousands of cancers would be missed by the test, making it inadequate as a screening tool for cancer.

Of course, the data from this pilot study will provide better insight into the true detection capability for the test, and the data will also allow for improvements that can make future tests far more accurate and reliable. We will have to keep tabs on this pilot study and come back in 2023 when preliminary data will be available for publication. 

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