Liquid Biopsy Testing

I am being asked more and more about liquid biopsy testing and wanted to share information to consider and discuss with your medical team.

Precision testing for treatment decision-making and monitoring in breast cancer has become more common in recent years. With the advent of ctDNA blood tests—circulating tumor DNA—it is possible to identify whether there are active, growing cancer cells circulating around the body (Minimal Residual Disease), and profile genomic targets.

By seeing the testing results, your doctor can know if a current treatment is having an effect. These tests can also find drug targets for new drugs, thus changing the treatment course to something more effective. For women with metastatic disease who have been given many treatments already, these tests are a game-changer. Plus, a blood test can be less invasive than a needle biopsy (and require no recovery time), thus reducing trauma. 

There are many tests available, but if you are going to discuss getting tested with your medical team, know which ones are clinically validated and will give information that is actionable. Clinically validated tests have been rigorously tested in large groups, are FDA-approved, and have been evaluated enough to be part of national cancer care guidelines. These tests are now used routinely in large cancer centers. Examples are Guardant360 CDx, FoundationOne Liquid CDx, and Signatera or Northstar (for Minimal Residual Monitoring).

With these validated tests, you can trust the result is real, not noise. The tests are designed to avoid false alarms, thus minimizing unnecessary scans, biopsies, anxiety, and treatments. Your doctor can clearly know what needs to be treated. Insurance coverage is not consistent, so be sure to explore what your insurance (or the testing company) will cover. If you have metastatic or recurred disease, ask your doctor about performing precision testing with ctDNA with the question, “What decision will this test help us to make?”

These tests are not as useful for very small or very early cancers, “just checking” for cancer, or for diagnosing a new mass. Early cancers don’t release enough DNA into the bloodstream to be detectable. A new mass will always need to be biopsied for accurate diagnosis. 

But for many people managing cancer, the new tests allow for a minimally invasive way to gain information about whether treatment is working, treatments that could work better, and if taking a break/stopping treatment is even an option.