Liquid Biopsies for Cancer: What to Know and What to Expect

November 3, 2022
Kate Ruder

Liquid biopsies are a type of test used to find cancer cells and cancer DNA in the blood. They are a less invasive alternative to other types of biopsies used to diagnose cancer. While liquid biopsies are still new and are not yet available for most types of cancer, they are being used more often for people with non-small cell lung cancer (NSCLC).

Here, you can learn the basics about liquid biopsies and what to expect if your doctor has recommended you receive this kind of test.

What are liquid biopsies?

A liquid biopsy is a blood test that detects cancer cells or DNA that are circulating in the blood, called “circulating tumor DNA” or “ctDNA.” Like healthy cells, cancer cells die and are replaced. When these dead cells break down, they are released from the tumor into the bloodstream. A liquid biopsy detects the small pieces of DNA in the bloodstream from these cancer cells.

Liquid biopsies are different from other types of biopsies, such as core needle biopsies and fine needle aspiration biopsies, which are the main way doctors diagnose and treat most types of cancer. During a needle biopsy, a doctor surgically removes a small amount of tissue from a tumor or suspicious area. Then, a pathologist examines the tissue under a microscope for the presence of cancer cells. A liquid biopsy, however, is performed using a simple blood draw. The blood sample is then sent to a laboratory for analysis.

Liquid biopsies can be done in addition to a tumor biopsy to support an initial cancer diagnosis and provide more information. They can also be used multiple times throughout treatment to monitor a tumor and see how well a specific treatment is working.

Why might I need a liquid biopsy?

Liquid biopsies may be an option along with other tests to guide cancer treatment decisions. Results from liquid biopsy tests can help your doctor recommend the best treatment specifically for your type of cancer. Liquid biopsies may also be an option if getting a tissue sample through a needle biopsy is not possible or if results are needed more quickly.

Currently, liquid biopsies are most commonly used to identify specific genetic changes in people with NSCLC (see below). However, they are also being studied and used for other types of cancer, including breast cancer, ovarian cancer, and prostate cancer.

What type of liquid biopsy might I receive?

There are several types of liquid biopsies that have been approved by the U.S. Food and Drug Administration (FDA). In the early 2000s, the FDA approved the first liquid biopsy test to monitor cancer in people with advanced breast cancer, colorectal cancer, and prostate cancer. This liquid biopsy, called the CellSearch Circulating Tumor Cell (CTC) test, analyzes a blood sample for the presence of circulating tumor cells. This type of monitoring can help your doctor evaluate how well a certain treatment is working and determine which follow-up tests may be needed.

In 2016, the FDA approved the cobas EGFR Mutation Test v2 liquid biopsy test that detects specific mutations, or changes, in the DNA from tumor cells circulating in the blood of people with NSCLC. By identifying these mutations, doctors can determine whether a type of treatment called targeted therapy may be helpful in treating the cancer. Targeted therapies work by targeting the specific mutations contributing to the cancer’s growth and survival.

In 2021, 2 other liquid biopsy tests have been approved by the FDA to detect mutations in the DNA from tumor cells in the blood. The Guardant 360 CDx test is approved for use in people with NSCLC, and the FoundationOne Liquid CDx is approved for use in people with NSCLC, prostate cancer, ovarian cancer, and breast cancer.

What can I expect if I am receiving a liquid biopsy?

To collect a sample for a liquid biopsy, a health care professional will use a needle to draw a small sample of blood from a vein, usually in your arm. This is the same type of blood draw you would receive if your doctor was doing other common tests, like a complete blood count. Then, your health care provider will send this to a laboratory for testing.

One advantage of a liquid biopsy is that it is a simple, noninvasive procedure. You do not need to take special precautions before or after your blood is drawn for a liquid biopsy, and your doctor will tell you if you need to stop taking any medications before having your blood drawn. While more and more public and private health insurance coverage includes liquid biopsies, you should always contact your insurance provider before getting a liquid biopsy to see whether your test will be covered under your plan.

What happens when liquid biopsy results come back?

Your doctor will typically receive the results from your liquid biopsy within 7 to 10 days. Your doctor will discuss with you the results of your liquid biopsy, what they mean for you, and what next steps are recommended, if needed.

For example, the results of your test may show that you have higher or lower counts of circulating tumor cells in your blood. That could indicate whether your cancer is shrinking from treatment or if you might need further tests, such as magnetic resonance imaging (MRI), to determine if the cancer has grown or spread. Meanwhile, the results of tests for mutations in tumor cell DNA can show whether your cancer may respond to certain targeted therapies. However, it is important to note that liquid biopsy tests for mutations in tumor cell DNA can sometimes give false-negative results. That means the result may come back negative even though there are mutations in your tumor’s DNA that could respond to targeted therapies. In this case, doctors often recommend a follow-up tissue biopsy to determine the best treatment option. Always talk with your doctor if you have any questions about the results of your liquid biopsy.

What other research is being done around liquid biopsies?

Liquid biopsies are being studied to see if they can help detect cancer recurrence in people who have previously received cancer treatment. Researchers are also studying how liquid biopsies can be used to precisely monitor how well tumors respond to treatment before these changes can be seen on imaging tests, such as on MRI scans. Finally, researchers are studying how liquid biopsies can be used to detect cancer in its earliest stages and to detect cancers that do not yet have routine screening tools.

Always talk with your doctor if you have any questions about the testing they recommend for you, including if that testing includes a liquid biopsy.

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