Liquid biopsy in metastatic breast cancer

A liquid biopsy is a blood test that looks for small fragments of DNA shed by cancer cells into the bloodstream, called circulating tumour DNA. In metastatic breast cancer, it is mainly used to find gene changes, or mutations, that can guide the choice of targeted treatment, such as changes in the PIK3CA, ESR1 or BRCA genes. It avoids the need for a new tissue biopsy in many cases, and because cancer anywhere in the body can shed DNA into the blood, it can pick up mutations that a single tissue sample might miss. It does not replace scans for checking how the cancer is responding, and it is not a screening test for healthy people.

Why it has become important

Newer treatments for metastatic breast cancer work best in cancers with particular mutations. Some mutations, such as in ESR1, develop during treatment, so testing may need to be repeated when the cancer grows.

What it can find

Mutations that make certain targeted treatments more likely to help, and sometimes changes that explain why a treatment has stopped working.

Its limits

If the cancer sheds very little DNA, the test may not find a mutation that is present. A negative result therefore sometimes leads to a tissue test as well.

A liquid biopsy is a useful tool for guiding treatment in metastatic breast cancer, but it answers specific questions. It is not a general test of how much cancer is present or whether treatment is working.

A negative result is not always final

Low levels of tumour DNA can make mutations hard to detect. If no mutation is found, your oncologist may suggest a tissue test, or repeating the blood test later.

Unexpected findings

Sometimes a result suggests a change that could be inherited, or finds changes from blood cells rather than the cancer. Your team may recommend genetic counselling or further tests to clarify.

Not for screening or routine monitoring

Liquid biopsy is not currently recommended to screen healthy people or to replace scans in routine follow-up after early breast cancer.

What this page cannot tell you

It cannot tell you whether testing would change your treatment. Ask your oncologist what they hope to learn from it.

Liquid biopsy tests are offered by several laboratories in India, but they differ in which genes they test, how sensitive they are and how much they cost.

Ask what the test covers

Some tests look at a few genes, others at many. Your oncologist can advise which test answers the question relevant to your treatment.

Check cost and coverage

These tests can be expensive and are not always covered by insurance. Ask for an estimate and check coverage before testing.

Choose accredited laboratories

Using laboratories with recognised quality accreditation helps ensure reliable results.

Research is exploring new uses of liquid biopsy in breast cancer, though these are not yet part of routine care.

Detecting recurrence earlier

Studies are testing whether tumour DNA in the blood can signal a return of cancer before scans or symptoms after early breast cancer.

Guiding treatment after surgery

Trials are also asking whether finding tumour DNA after surgery could identify women who would benefit from extra treatment, and spare others from treatment they do not need.

Tracking response

Changes in tumour DNA levels during treatment may one day help show whether a treatment is working sooner than scans.