What Is a Liquid Biopsy?

Medically Reviewed by Sabrina Felson, MD on March 14, 2024
4 min read

A liquid biopsy is just a sample of your blood, usually taken from a vein in your arm. Doctors use it to check for cancer cells or pieces of DNA from a tumor. The sample can help them detect breast cancer and figure out the best treatment. If you’ve had breast cancer before, a liquid biopsy may help doctors predict if it’ll come back.

Doctors first used liquid biopsy on blood cancers like leukemia, lymphoma, and multiple myeloma. Now they can use it on cancers with solid tumors, such as:

  • Breast cancer
  • Colorectal cancer
  • Bladder cancer
  • Prostate cancer
  • Pancreatic cancer
  • Melanoma
  • Lung cancer

A liquid biopsy is a much easier and simpler way of figuring out what’s happening than a surgical biopsy, which is more invasive. That’s because cancers release bits of DNA carrying mutations into your blood. With a liquid biopsy, a doctor can look for these mutated DNA pieces as a sign there’s cancer in your body. Most commonly, liquid biopsy checks for:

  • Circulating tumor DNA (ctDNA)
  • Circulating cell-free RNA (cfRNA)
  • Circulating tumor cells (CTCs)
  • Extracellular vesicles (EVs)
  • Tumor-educated platelets (TEPs)
  • Certain proteins
  • Metabolites -- substances released during cell metabolism

A liquid biopsy can:

  • Diagnose your cancer earlier than other methods such as radiology or imaging
  • Help doctors form treatments specific to your cancer
  • Help doctors figure out which therapies won’t work because of your cancer’s makeup
  • Measure if there is cancer left after treatment, and if so, how much
  • Figure out whether your cancer has come back or why it’s resistant to treatment

Research is ongoing, but early data show that liquid biopsy may help predict survival outcomes and risk of recurrence (the chance of your cancer coming back).

Experts are still researching how liquid biopsy can be used to diagnose early or localized breast cancer. Currently, it’s most helpful for:

Metastatic breast cancer. The FDA has approved liquid biopsy as a way to decide on a targeted treatment for metastatic breast cancer. Doctors look for mutations in a specific gene called PIK3CA. If they find it, they can prescribe a medication called alpelisib (Piqray). This medication is typically used in combination with fulvestrant (Faslodex) in men or postmenopausal women whose metastatic breast cancers are:

Doctors can also use the number of CTCs in people with metastatic breast cancer to help predict the prognosis or outcome.

HR-positive breast cancer. In a small study, doctors found that women with HR-positive breast cancer who had circulating cancer cells had a higher risk of their cancer returning. The same wasn’t true for women with HR-negative cancer. The presence of CTCs didn’t raise their chance of recurrence.

Liquid biopsy isn’t used as commonly in breast cancer as it is in other types of cancer. Tissue biopsy is more typical. But liquid biopsy has some benefits, especially compared to tissue biopsy. These include:

Easy to repeat. Tissue biopsies are invasive, costly, and time-consuming. Your doctor can easily take multiple liquid biopsy samples over time.

Tracks cancer in real-time. Because they can take several biopsies, doctors can use the test to better understand what kind of molecular changes might be happening in a tumor and see whether treatment is working.

Helps you avoid unnecessary treatments. By looking at which gene mutations your cancer cells have, your doctor can narrow down which drugs are most likely to target your cancer.

Less risky. Tissue biopsy comes with a risk of tumor spread, injury to nearby tissue, and severe bleeding.

Results come quickly. Typically in 7-10 days.

No prep. You typically don’t have to prepare for a liquid biopsy. But you may need to stop taking certain medications a few days beforehand. Your doctor will let you know.

You might also have more tumors that make tissue biopsy less safe. Liquid biopsy gives your doctors an alternative option for gathering information on your metastatic breast cancer.

But there are drawbacks:

It’s less effective for early-stage or localized disease. So far, liquid biopsies don’t detect early or localized breast cancer better than mammograms.

It can miss markers. The number of circulating tumor cells (CTCs) in an average blood sample is extremely low. The test isn’t always sensitive enough to detect them or other signs of cancer.

False positives. Older cells can form abnormalities that look like signs of cancer.

Not helpful if you have more than one type of cancer. The test can only tell your doctors if signs of cancer are present. It can’t tell them which cancer those cells came from.