Liquid Biopsy for Breast Cancer: What a Blood Test Can Tell You
A liquid biopsy is a test that looks for cancer-related material circulating in body fluids, most commonly blood. In breast cancer, the main focus is circulating tumor DNA (ctDNA), which consists of small DNA fragments released by cancer cells into the bloodstream.
 
Unlike a tissue biopsy, liquid biopsy usually requires only a blood sample. Its clearest established role in breast cancer is in advanced or metastatic disease, where ctDNA testing may identify tumor-related genetic alterations that can help guide treatment.
 
Key Takeaways

• Liquid biopsy can analyze cancer-related DNA circulating in the blood.
• In metastatic breast cancer, ctDNA may identify mutations that influence treatment choices.
• A negative liquid biopsy does not rule out a relevant tumor mutation.
• Liquid biopsy does not replace tissue biopsy for diagnosing breast cancer.
• It is not a replacement for mammography or other established breast cancer screening.
• Its role in detecting recurrence after early breast cancer treatment is still being studied.

 

What does a liquid biopsy detect?
Normal cells release small DNA fragments into the bloodstream. This is called cell-free DNA (cfDNA).
 
Cancer cells can also release DNA. The cancer-derived portion is known as circulating tumor DNA (ctDNA).
 
Using techniques such as next-generation sequencing (NGS), laboratories can perform genomic testing on ctDNA and look for multiple cancer-related genetic alterations at the same time.
 

How is liquid biopsy used in breast cancer?
Its strongest current role is in advanced or metastatic breast cancer.
Cancer can develop new molecular changes as it progresses or is exposed to treatment. Liquid biopsy can sometimes provide updated information about these changes without requiring another tumor biopsy.
 
For example, ctDNA testing may identify:

• PIK3CA mutations, which can help determine whether certain patients with hormone receptor-positive, HER2-negative advanced breast cancer may be candidates for targeted treatment.
• ESR1 mutations, which can develop during endocrine therapy and may influence subsequent treatment decisions in selected patients with estrogen receptor-positive, HER2-negative metastatic breast cancer.

 
This is part of precision oncology, in which treatment decisions increasingly consider the individual molecular characteristics of a cancer.
 

Can liquid biopsy replace a tissue biopsy?
No.
A tissue biopsy remains essential for confirming a new breast cancer diagnosis and determining important features such as tumor type, grade, estrogen receptor (ER), progesterone receptor (PR) and HER2 status.
In advanced cancer, ctDNA may provide additional genomic information when tumor tissue is unavailable, difficult to obtain or when updated molecular profiling is needed.
However, some cancers release only small amounts of DNA into the bloodstream. A negative ctDNA result therefore does not necessarily mean that a relevant mutation is absent, and tissue testing may still be required.
 

Can liquid biopsy detect breast cancer recurrence earlier?
This is an important area of ongoing research.
After treatment for early-stage breast cancer, very small amounts of cancer may sometimes remain in the body. This is known as molecular residual disease (MRD).
Studies have shown that detecting ctDNA after treatment is associated with a higher risk of future recurrence and may sometimes identify molecular relapse before it becomes visible on imaging.
 
However, an important question remains: does changing treatment based only on a positive ctDNA result improve outcomes?
As of 2026, this has not yet been established. Clinical trials are continuing to evaluate how ctDNA-guided treatment could be used in early breast cancer.
 

Can liquid biopsy be used for breast cancer screening?
Not routinely.
Liquid biopsy should not replace mammography, breast ultrasound, MRI when indicated, or medical evaluation of a new breast symptom.
Detecting the very small amount of tumor DNA that may be present in early cancer remains technically challenging. Blood-based screening for breast cancer is therefore still under investigation.
 

Liquid biopsy and breast cancer care at Bumrungrad
At Bumrungrad International Hospital, the Breast Center works closely with the Horizon Regional Cancer Center, pathologists, radiologists and laboratory specialists to coordinate breast cancer diagnosis and treatment.
 
Bumrungrad offers next-generation sequencing (NGS)-based genomic testing through liquid biopsy for solid tumors. Testing may analyze ctDNA for cancer-related genetic alterations that could help guide targeted treatment in selected patients. Results are considered together with ER, PR and HER2 status, tumor stage, grade, pathology and imaging findings.
 
Bumrungrad Laboratory has maintained College of American Pathologists (CAP) accreditation since 2016 and provides advanced testing including DNA sequencing.
Bumrungrad’s Breast Cancer Program received JCI Clinical Care Program Certification in 2025. In Newsweek and Statista’s Best Specialized Hospitals Asia Pacific 2026, Bumrungrad ranked No. 1 in Thailand and 58th in Asia-Pacific for Oncology.
 

 
Frequently Asked Questions
Is liquid biopsy the same as inherited genetic testing?
No. Liquid biopsy generally looks for tumor-related alterations in ctDNA. Germline genetic testing looks for inherited variants, such as BRCA1 or BRCA2.
 
Does a negative liquid biopsy mean there is no cancer?
No. Some tumors release too little ctDNA to be detected reliably.
 
Can liquid biopsy replace mammography?
No. Liquid biopsy is not currently an established breast cancer screening test.
 
Medical references

1. Pascual J, Attard G, Bidard FC, et al. ESMO recommendations on the use of circulating tumour DNA assays for patients with cancer: a report from the ESMO Precision Medicine Working Group. Annals of Oncology. 2022;33(8):750–768.
2. Henry NL, Somerfield MR, Dayao Z, et al. Biomarkers for Systemic Therapy in Metastatic Breast Cancer: ASCO Guideline Update. Journal of Clinical Oncology. 2022;40(27):3205–3221.
3. Burstein HJ, DeMichele A, Somerfield MR, Henry NL. Testing for ESR1 Mutations to Guide Therapy for Hormone Receptor–Positive, HER2-Negative Metastatic Breast Cancer: ASCO Guideline Rapid Recommendation Update. Journal of Clinical Oncology. 2023;41(18):3423–3425.
4. Schlam I, Tolaney SM, Lin NU, Parsons H, Morganti S. Circulating Tumor DNA in Early Breast Cancer: A Review. JAMA Oncology. 2026;12(7):773–784.
5. Garcia-Murillas I, Chopra N, Comino-Méndez I, et al. Assessment of Molecular Relapse Detection in Early-Stage Breast Cancer. JAMA Oncology. 2019;5(10):1473–1478.
6. Bumrungrad International Hospital. Laboratory Service Guide: liquid biopsy and comprehensive genomic profiling tests.

 

Medically reviewed by:
Thiraphop Waipradab, M.D.
Breast Surgery & General Surgery
Last medically reviewed: September 2026