What is a liquid biopsy?

How it works

Tumors shed fragments of DNA into the bloodstream. Labs sequence the cell-free DNA (cfDNA) in a blood sample and look for signals that come from cancer: specific mutations, or chemical marks on DNA called methylation patterns. Austin is home to cfDNA laboratories run by Natera.

What it's used for

• Choosing treatment: identifying tumor mutations that match targeted therapies when tissue is hard to get.
• Monitoring: tracking whether tumor DNA falls or rises during and after treatment.
• Screening (emerging): looking for cancer in people without symptoms.

Where screening stands

In July 2024 the FDA approved Guardant Health's Shield blood test as a primary screening option for colorectal cancer (ASCO Post). Reporting on the approval noted it detected 83% of colorectal cancers but only 13% of precancerous polyps (Harvard Health), so it doesn't replace colonoscopy's ability to find and remove polyps.

No test for screening many cancers at once is FDA-authorized yet. An FDA panel voted in favor of GRAIL's Galleri test in September 2026; read what the data show.

Not every non-invasive cancer test is a liquid biopsy

San Antonio's bioAffinity Technologies, for example, analyzes sputum (not blood) with flow cytometry and AI to look for lung cancer. Different sample, different technology, similar goal.

Limits to keep in mind

• A negative result doesn't rule out cancer, especially early-stage cancer that sheds little DNA.
• A positive screening result needs diagnostic follow-up such as imaging or a tissue biopsy.
• Talk to a clinician about which tests fit your risk and history.