What is a liquid biopsy?

A liquid biopsy uses a sample of body fluid—most often blood, and sometimes other fluids such as urine, saliva, or other secretions—to look for small fragments of genetic material or other substances that may be released by cancer cells.

Unlike a tissue biopsy, a liquid biopsy does not remove a piece of a tumor. Instead, it analyzes biomarkers that may be circulating in the body. This can include fragments of DNA, RNA, or other markers linked to cancer.

Liquid biopsies may be used alongside tissue biopsies to provide additional molecular information, or in situations where collecting tissue is difficult, not possible, or when a care team monitors specific biomarkers over time. Because liquid biopsies involve a fluid sample, they may be repeated more easily in certain situations compared to a tissue biopsy.

Research into how liquid biopsies can be used is ongoing. While some tests are already FDA-approved for specific uses in certain cancers, scientists are continuing to explore their use in other areas of cancer care. This includes research into developing tests that may help detect signals linked to multiple types of cancer from a single blood sample (sometimes called multi-cancer early detection).

As more research becomes available, these approaches are being tested to better understand how they could be used alongside existing screening and diagnostic tools.

Learn about The search for a ‘liquid biopsy’ and other advances to diagnose cancer .

The key differences between liquid and tissue biopsies

Tissue and liquid biopsies differ in several important ways, which can help explain your care team’s decision to use one type instead of, or alongside, the other.

Sample type:

• Tissue biopsies use samples taken from a piece of tumor or affected tissue.
• Liquid biopsies use samples taken from body fluids, most commonly blood.

How samples are collected:

• Tissue biopsies may involve a procedure in which a small sample is taken using a needle or a minor surgical procedure.
• Liquid biopsies are often less invasive and usually require the collection of a blood sample.

Type of information gathered:

• Tissue biopsies allow pathologists to directly examine cells to see if they are cancerous, help identify the origin (cancer type), and may provide information about features linked to how the cancer may behave.
• Liquid biopsies analyze biomarkers that may provide information about a known or suspected cancer. These biomarkers may come from cancer cells or from the body’s response to cancer.

When they are used:

• Tissue biopsies are often used to help confirm a diagnosis and provide information that may help in cancer classification and staging when considered with other clinical tests.
• Liquid biopsies are often used after a cancer diagnosis to provide additional information or look for changes over time. They may also be used when a tissue biopsy is not possible.

Limitations:

• Tissue biopsies sample one area, so they may not capture every genetic difference across a tumor or among different tumor sites. This is known as tumor heterogeneity, meaning that different parts of a tumor or different tumor sites may have different features.
• Liquid biopsies may miss findings when there are very low levels of circulating tumor DNA (small pieces of cancer-related DNA found in the blood). This means that a negative liquid biopsy result does not rule out cancer and would be considered alongside other clinical information.

Each biopsy type has its advantages and limitations, and no single test can answer every question about a given cancer on its own. Your care team may recommend one or both types of biopsies to appropriately inform your cancer care plan.