Liquid Biopsy

A liquid biopsy is a blood test that detects signs of cancerous tumors, including tumor cells and cancer cell DNA. Current U.S. FDA-approved tests can detect some types of advanced cancers, predict prognosis and help healthcare providers make treatment decisions. Research is ongoing to explore additional uses of liquid biopsy tests.


What is a liquid biopsy?

A liquid biopsy is a blood test that detects cancerous tumors. As a tumor grows, pieces can break off and circulate in your bloodstream. A liquid biopsy can identify those pieces. Liquid biopsies can detect:

  • Circulating tumor cells (CTCs): A CTC is a cancer cell from the tumor that’s traveling in your bloodstream.
  • Circulating tumor DNA (ctDNA): ctDNA is a DNA fragment from the tumor cell circulating in your blood. DNA contains the genetic code, or instructions, that control a cell’s behavior.

CTCs and ctDNA in your blood provide evidence that you have a cancerous tumor. These pieces of your tumor also provide genetic information about the cancer that can help your healthcare provider decide what treatments may work best to treat it.

Liquid biopsy is a relatively new test with several potential groundbreaking uses in cancer treatment, with a few U.S. Food and Drug Administration (FDA)-approved uses. Research into its benefits is ongoing.

How is a liquid biopsy different from a biopsy?

Unlike a biopsy, liquid biopsies don’t test tumor tissue directly. Instead, they test for evidence of a tumor. During a biopsy, your healthcare provider removes a tissue sample from a tumor and tests the cells in a lab to see if they’re cancerous. In contrast, a liquid biopsy detects signs of a tumor, like tumor cells and tumor DNA.

A biopsy is considered the “gold standard” when diagnosing cancer. It’s the best procedure available for diagnosing cancer.

With a liquid biopsy, even if you have a tumor, there’s no guarantee that signs of that tumor will be detectable in a single blood sample. Still, when liquid biopsies detect cancer, they provide valuable information about cancer cells that can help your healthcare provider plan treatment.


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When is a liquid biopsy performed?

Your healthcare provider may recommend a liquid biopsy if you have metastatic cancer and current treatments aren’t working. Metastatic cancer is advanced cancer. Metastasized cancer has spread from the original tumor site to other parts of your body. As it spreads, tumor pieces break off and travel through your bloodstream.

Your provider may order a liquid biopsy to:

  • Determine your prognosis. Liquid biopsies can identify CTCs associated with many cancers. Having fewer tumor cells is associated with a better outcome than having many tumor cells. Your healthcare provider can perform periodic tests to monitor your condition and adjust treatment as needed.
  • Make treatment decisions. Liquid biopsies can show if you’re a good candidate for certain types of targeted therapy treatments. Targeted therapy is a type of cancer treatment designed to destroy certain types of cancer cells. For example, a cancer cell may have an error in its DNA that a specific targeted therapy is designed to attack. A liquid biopsy can detect these errors. In turn, your healthcare provider may prescribe a treatment that targets that error.

You may also receive a liquid biopsy if you can’t have a traditional biopsy to diagnose cancer. A biopsy is a much more invasive procedure than a liquid biopsy. You may not feel well enough to have a biopsy. Depending on where your tumor is located, your provider may not be able to access it without potentially damaging surrounding organs.

What liquid biopsy tests are FDA-approved?

FDA-approved tests have been thoroughly researched to ensure they’re safe and accurate. Several liquid biopsy tests are under development and in various stages of research. Four are FDA-approved:

  • Cell Search® Circulating Tumor Cell (CTC) Test detects CTCs. It’s used to predict the likely outcome for people with metastatic breast, prostate or colon cancer. It can help your provider monitor your condition. Few CTCs in the blood are a sign of a favorable prognosis. Many CTCs in the blood are a sign of an unfavorable prognosis.
  • cobas® EGFR Mutation Test v2 detects ctDNA. It detects a mutation (error) on the EGFR gene that’s common in non-small cell lung cancer (NSCLC). This information can help your healthcare provider decide which types of treatments will work best to target the cell error.
  • Guardant360® CDx detects ctDNA. It’s also used to detect common genetic errors. It can help your provider choose the most effective treatments.
  • FoundationOne® Liquid CDx detects ctDNA. It detects mutations in various cancers that can help your provider determine which treatments might work best.


Test Details

How does a liquid biopsy test work?

A liquid biopsy test involves a simple blood draw. Your healthcare provider will take a blood sample and send it to a lab for testing. In the lab, a machine will separate the blood cells (the solid part of your blood) from the plasma (the liquid part of your blood). A specialist trained to analyze fluid and tissue samples for signs of disease (pathologist) will look for CTCs or ctDNA in the plasma.

Is liquid biopsy painful?

A liquid biopsy feels like having your blood drawn. You may feel a slight prick or sting when the needle enters your arm, but the discomfort usually goes away quickly.

One of the advantages of a liquid biopsy is that it’s much less invasive and painful than a biopsy.


Results and Follow-Up

What do the results mean?

Test results reveal if your blood sample is positive or negative for CTCs or ctDNA. If you’re positive, the tests can help your healthcare provider determine your cancer type. Tests that look for ctDNA can identify common genetic errors associated with certain types of cancer.

When should I know the results of the test?

The results should be ready within two to three weeks.

How accurate is a liquid biopsy?

FDA-approved liquid biopsies effectively do what they say they do. CTC tests allow your healthcare provider to predict your prognosis and monitor your condition. ctDNA tests can identify genetic errors in cancer cell DNA, guiding your provider’s treatment decisions.

A liquid biopsy isn’t always reliable when it comes to diagnosing cancer. A standard biopsy is needed to confirm a cancer diagnosis.

A note from Cleveland Clinic

Liquid biopsy tests are an active area of research and development because of their potential to help providers diagnose and monitor cancer with a simple blood test. Research is underway to develop liquid biopsy tests that can do things traditional biopsy procedures can’t do, like detect cancer before a tumor has formed. Still, more research is needed to understand the potential uses of liquid biopsy. They can detect certain cancers and inform treatment decisions in particular situations. In the future, they may have many more uses.


Medically Reviewed

Last reviewed on 08/11/2022.

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