How Does Liquid Biopsy Detect Cancer?

Liquid biopsies are blood tests that can spot cancer signs, like tumor cells and cancer DNA. They’re approved by regulators such as the U.S. FDA for some advanced cancers, helping with prognosis and treatment decisions. 

Liquid biopsies can identify two things: circulating tumor cells (CTCs) that are cancer cells from the tumor in your bloodstream. The other is circulating tumor DNA (ctDNA) which is DNA fragments from the tumor cell circulating in your blood, carrying genetic information.

CTCs and ctDNA indicate a cancerous tumor and provide genetic data to guide treatment choices. Liquid biopsy is promising in cancer treatment, with some FDA approval, and ongoing research for more applications.

What Is The Difference Between Liquid Biopsy And A Biopsy?

Liquid biopsies and traditional biopsies have a couple of differences. Traditional biopsies require a tissue sample from a tumor for direct testing in a laboratory. Whereas, liquid biopsies for cancer detection work differently. They don’t examine tumor tissue directly but instead look for evidence of a tumor’s presence in your bloodstream.

Traditional biopsies are widely regarded as the “gold standard” for diagnosing cancer, as they provide an accurate and comprehensive assessment of cancer cells. In contrast, liquid biopsies may not always detect signs of a tumor in a single blood sample. 

However, when they do identify cancer-related indicators, such as tumor cells and DNA, they offer valuable insights that can assist  healthcare providers in planning appropriate treatments.

Liquid biopsies are a less invasive means of searching for tumor-related markers, while traditional biopsies remain the most reliable method for diagnosing cancer. Both approaches serve vital roles in cancer diagnosis and treatment planning.

When To Get a Liquid Biopsy?

In cases of metastatic cancer, an advanced form of cancer, when conventional treatments prove ineffective, your healthcare specialist might suggest a liquid biopsy. Metastatic cancer involves the spreading of cancer from its origin to other parts of the body. During this type of cancer, tumor fragments circulate through your bloodstream.

Liquid biopsies can be useful during:

  • Determining Prognosis: Liquid biopsies can identify circulating tumor cells (CTCs) associated with various cancers. A lower number of CTCs is generally a good prognosis. Periodic tests using liquid biopsies allow healthcare specialists to monitor your condition and make treatment adjustments as necessary.
  • Treatment Decision-making: Liquid biopsies can provide information on whether you are a suitable candidate for specific types of targeted therapy treatments. Targeted therapy is designed to target particular cancer cell types. For instance, if a cancer cell has a DNA error that can be targeted by a specific therapy, a liquid biopsy can detect this error.

Additionally, liquid biopsies can be an alternative if you cannot undergo a traditional biopsy. Traditional biopsies are more invasive and you might not be in a good enough physical state to get one. 

Depending on the location of the tumor, accessing it with a traditional biopsy might risk damaging surrounding organs. In such cases, a liquid biopsy offers a less invasive and viable diagnostic option.

Types Liquid Biopsy Tests Available

The FDA has rigorously evaluated several liquid biopsy tests to ensure their safety and accuracy. Currently, four liquid biopsy tests have received FDA approval:

  • Cell Search® Circulating Tumor Cell (CTC) Test: This test is designed to detect CTCs, particularly in cases of metastatic breast, prostate, or colon cancer. It helps predict the likely outcome for patients and allows healthcare providers to monitor their condition. A lower count of CTCs in the blood suggests a more favorable prognosis, while a higher count indicates an unfavorable prognosis.
  • cobas® EGFR Mutation Test v2: This test focuses on detecting ctDNA and specifically a mutation on the EGFR gene commonly found in non-small cell lung cancer. This information is valuable when deciding on the most effective treatments that target the identified genetic error.
  • Guardant360® CDx: This test also detects ctDNA and is used to identify common genetic errors. 
  • FoundationOne® Liquid CDx: This test is designed to detect ctDNA and identify mutations in various types of cancers. 

These FDA-approved liquid biopsy tests are valuable tools in cancer diagnosis and treatment. They offer a less invasive and efficient means of obtaining essential genetic information for personalized treatment approaches.

How To Do A Liquid Biopsy?

A liquid biopsy test is a relatively simple procedure. Here’s how it works:

  • Collecting Blood: Your healthcare provider will draw a blood sample, typically from a vein in your arm.
  • Lab Testing: This blood sample is then sent to a laboratory for analysis.
  • Blood Separation: In the lab, a machine is used to separate the blood into two components: the solid part, which consists of blood cells, and the liquid part, known as plasma.
  • Analysis by a Pathologist: A specialized pathologist, trained to examine fluid and tissue samples for signs of disease, will analyze the plasma for the presence of circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA).

Deciphering The Test Results 

Liquid biopsy test results provide valuable information about the presence or absence of circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) in your blood.

If your test shows a positive result, it helps identify:

  • Cancer Type: Positive results can help identify the type of cancer you have, aiding in the diagnostic process.
  • Genetic Errors: Tests that detect ctDNA are particularly useful in identifying common genetic errors associated with specific cancer types. This information is crucial for tailoring treatment plans to target these genetic abnormalities effectively.


Liquid biopsies are a less invasive and accessible method for cancer diagnosis and treatment. They detect circulating tumor cells and circulating tumor DNA in a simple blood draw, offering insights into cancer types and genetic errors. 

Liquid biopsies aid prognosis, guide treatment choices, and hold promise for personalized therapies. It is simple and accessible for all and represents a hopeful future in the battle against cancer.

Frequently Asked Questions

Is a liquid biopsy painful?

A liquid biopsy is generally not painful. You might experience a slight prick or sting when the needle enters your arm, but any discomfort usually fades quickly. One of the key benefits of a liquid biopsy is that it’s significantly less invasive and painful compared to a standard biopsy.

How accurate is a liquid biopsy?

FDA-approved liquid biopsies serve their intended purposes effectively. CTC tests predict prognosis and monitor your condition, while ctDNA tests identify genetic errors in cancer cell DNA, guiding treatment decisions. However, a liquid biopsy may not always provide a definitive cancer diagnosis thus eventually requiring a standard biopsy for confirmation.

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