Liquid Biopsy
What is a liquid biopsy?
A liquid biopsy is a blood test that analyzes fragments of tumor DNA (called circulating tumor DNA, or ctDNA) shed by cancer cells into the bloodstream. It is a less invasive alternative — or complement — to tissue biopsy, and can be repeated more easily over time.
For MET-altered cancers, liquid biopsy can detect MET exon 14 skipping mutations, MET amplification, and MET resistance alterations. It is particularly useful when a tissue sample cannot be obtained, or when monitoring for disease progression or resistance.
What liquid biopsy can and can’t do
Liquid biopsy is often used as a first step when tissue is unavailable, or as a complement to tissue testing to detect alterations that may not be captured in a single tumor sample. Because it reflects DNA circulating from all tumor sites, it can sometimes detect heterogeneity that a tissue biopsy from one location would miss.
However, liquid biopsy is not equally reliable for all alterations. MET overexpression cannot be detected in blood — it requires IHC testing on tumor tissue. Some MET exon 14 skipping alterations may be missed by DNA-based blood tests. A negative liquid biopsy does not rule out a MET alteration; tissue testing may still be needed.
A negative blood test is not a final answer.
If your liquid biopsy comes back negative for a MET alteration but you have clinical reasons to suspect one, ask your oncologist about tissue-based testing. The two approaches are complementary, not interchangeable.
When liquid biopsy is most useful
At progression: liquid biopsy is particularly valuable when cancer progresses on treatment, as it can rapidly identify new resistance alterations — including acquired MET amplification — without requiring a new invasive biopsy.
When tissue is insufficient: if initial biopsy material has been used up or a re-biopsy is not feasible, a liquid biopsy can provide molecular information to guide next treatment decisions.
For monitoring: some oncologists use serial liquid biopsies to track how tumor DNA levels change during treatment, which can signal early response or emerging resistance.
Commercially available tests
Several FDA-authorized liquid biopsy tests are available, including FoundationOne Liquid CDx and Guardant360 CDx. Ask your oncologist or molecular pathologist which test is most appropriate for your situation and what your insurance covers.