In 1869, an Australian physician called Thomas Ashworth was examining a blood sample from one of his deceased cancer patients when he noticed a cluster of cells that looked just like the original tumour. He had made a major scientific breakthrough.
What he had discovered is that cancer deposits genetic material into the bloodstream. This takes two forms.
DNA fragments from dead cells are released as what is known as circulating tumour DNA (ctDNA). This is because cancer not only accelerates cell division, but also cell death.
Sometimes whole cells break from the tumour as well. These are known as circulating tumour cells (CTC).
However, it took almost two centuries before medical practitioners were able to use Ashworth’s findings to develop a blood test (liquid biopsy) that could potentially diagnose and treat cancer more quickly and effectively than a surgical biopsy (taking tissue samples). As ctDNA represents just a small fragment of a person’s total circulating DNA, medicine had to wait until the technology became advanced enough to not only detect it and but also evaluate it to the required degree of sensitivity.
The US Food & Drug Administration (FDA) approved the first diagnostic molecular test based on liquid biopsy samples in 2016. Since then, it has started to become a more mainstream diagnostic tool for a whole range of cancers including: breast, colon, lymphoma, lung, melanoma and thyroid.
Clinicians use liquid biopsies to analyse a tumour’s molecular profile in order to personalise therapies. However, there is still one big limitation.
It is possible to miss the cancer if ctDNA levels are low. This is why surgical biopsies remain important and mandatory in most cancer cases.
However, in mid-June, Cancer Research UK announced that it was entering clinical trials for a test that is up to 10 times more sensitive than current methods. This one is able to find one mutant piece of DNA among a million and scan for thousands compared to the present 10 to 100 levels.
Here are some of the main benefits that liquid biopsies offer:
- More patients can be assessed - One of the biggest issues with surgical biopsies is that certain tumours are inaccessible such as those in the brain, for example. Some tumours are also too small to get a tissue sample. About 30% of non-small cell lung cancer patients fall into this latter category.
- They are non-invasive - They are a far more patient-friendly option than surgery. Taking someone’s blood is far quicker, simpler, cheaper, pain- and risk-free than putting them under the knife. Liquid biopsies are particularly beneficial for patients who are too ill to undergo surgery.
- They provide a more complete picture - A surgical biopsy provides a static and partial view of a single tumour. Liquid biopsies can identify potential secondary tumours and also enable practitioners to give a far more accurate staging of how far advanced a cancer is.
- They are more flexible - Liquid biopsies can be taken multiple times given how simple it is to draw blood. This is vital since cancer is not a stationary disease, but evolves all the time. Liquid biopsies, therefore, enable physicians to stay one step ahead. By constantly monitoring a patient’s blood, they can tell if a treatment plan is working, or a new one is required because the cancer has mutated and the drugs are no longer effective. The result is a far more tailored approach to an individual’s treatment needs.
- They might prevent relapse - The technology is now becoming so sophisticated that liquid biopsies can potentially pick up a relapse before there are even clinical symptoms. Physicians can actively monitor patients who are in remission, but whose blood samples pinpoint a higher risk of relapse.