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What Is a Liquid Biopsy?

A diagram showing a liquid biopsy's targets.
Credit: Technology Networks
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Liquid biopsies offer the potential to transform cancer care. In recent years, this minimally-invasive test is starting to replace invasive techniques for diagnosing and monitoring cancers.1

Liquid biopsies can be used to find cancer at an early stage, inform treatment decisions – or find out how well treatment is working or if the disease has returned.2 A big advantage is the potential to detect disease progression or resistance to treatment long before symptoms arise or it can be detected on imaging scans.

What is a liquid biopsy?

As a tumor grows, it starts to release materials – such as intact cancer cells3 or nucleic acids4 – into a person’s body fluids. A liquid biopsy is a laboratory test carried out on a sample of body fluid – such as blood, urine or saliva – to detect and analyze materials shed from the primary tumor and its metastases.

An image showing the key targets of a liquid biopsy.Figure 1: The liquid biopsy. This test targets various markers released from tumors that then circulate through the body. Here, a tumor releases markers into the bloodstream. These include circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating miRNAs and tumor-derived extracellular vesicles (EVs). They can be separated from blood cells for analysis, as seen in the tube on the right-hand side of the image. Credit: Technology Networks.

Liquid biopsy approaches include the analysis of:

  • Circulating tumor cells (CTCs)
  • Circulating tumor DNA (ctDNA)
  • Circulating miRNAs 
  • Tumor-derived extracellular vesicles (EVs).5

The results may reveal additional details about the tumor, such as the presence of specific molecular alterations, enabling doctors to devise personalized treatment strategies.

Liquid biopsy definition

A liquid biopsy is a rapid, simple alternative to standard tissue biopsies – providing a tool for obtaining diagnostic information about a person’s cancer.5 It is a minimally-invasive procedure and can be serially repeated, enabling doctors to get information about the tumor in real-time.5

Liquid biopsy vs. tissue biopsy

A tissue biopsy is currently the ‘gold standard’ test for diagnosing cancer. It involves a surgical procedure to remove a tissue sample – for example, from a suspicious lump or growth – which is then sent for microscopic examination to confirm the presence of cancerous cells. Other tests, such as genetic sequencing, may also be carried out on the sample to provide more information to help guide treatment decisions. But it can be an invasive procedure – especially for tumors that are difficult to access, such as those located deep inside the body or close to vital organs. This can limit opportunities to collect multiple samples to look for changes over time – for example, to quickly find out whether a treatment is working or if the disease has developed resistance.

In contrast, a liquid biopsy looks for evidence of cancer somewhere in the body even if its location is unknown. The test involves taking a sample of a body fluid, often a small blood sample, which is then sent to the laboratory for testing. As a liquid biopsy is a much simpler and less invasive procedure than a standard tissue biopsy, it is easier to collect samples much more frequently – enabling doctors to monitor the disease more closely and adjust treatment as needed.

A liquid biopsy may also reveal more information about the complexity of an individual’s cancer than a tissue biopsy. As a tumor grows, it evolves – and so most are made up of a patchwork of cancer cells with different genetic alterations. As a result, testing one tissue sample collected from a single region of a tumor is unlikely to capture a fully comprehensive picture of the disease. However, as liquid biopsies detect materials shed from different parts of a tumor and its metastases, they are more likely to provide a window into the evolving molecular landscape of the disease.