Medically Reviewed by: Charles H. Weaver, MD
Over the past five years, CancerConnect’s online community has received thousands of questions from patients and caregivers trying to understand ctDNA and minimal or molecular residual disease (MRD) testing and what these results really mean for their care. ctDNA‑based MRD testing is increasingly used to help doctors detect tiny amounts of remaining cancer, estimate the risk of recurrence, and personalize decisions about treatment and follow‑up. This FAQ was created to answer the most common questions asked and to help you feel more informed and prepared when you talk with your care team about MRD testing.
What is ctDNA and MRD testing?
Minimal or molecular residual disease (MRD) is the term doctors use when a very small amount of breast cancer remains after treatment—too little to be seen on scans or felt on exam, but still important to detect. Circulating tumor DNA (ctDNA) refers to tiny fragments of tumor DNA that breast cancer cells release into the bloodstream. ctDNA based MRD testing is a blood test designed to pick up these small traces of cancer DNA, which is a sign that cancer is still present in the body and is likely to recur even when imaging looks normal.
How can ctDNA and MRD testing help people with breast cancer?
For breast cancer, ctDNA and MRD testing can help show whether very small amounts of cancer may still be present after you finish treatment, even when scans and exams look normal. This extra information can help your care team better understand your personal risk of recurrence and decide how closely to monitor you and whether additional treatments—such as endocrine therapy, targeted therapy, chemotherapy, or clinical trials—might be helpful for your specific situation.
When is ctDNA based MRD testing usually considered in breast cancer?
Doctors best utilize ctDNA‑based MRD testing when obtained at the time of initial diagnosis. This helps determine prognosis, allows them to monitor response to treatment and check for any remaining cancer cells that are too small to see on imaging. Testing is typically performed at regular intervals during follow‑up visits to look for early signs of recurrence or to track how well systemic treatments (like chemotherapy, targeted therapy, or immunotherapy) are working.
In some settings, it may also be used at specific follow up time points or in certain metastatic cases to help look for early signs that cancer could be returning or to monitor how well treatment is working.
Can ctDNA/MRD testing help decide if I need more treatment after finishing standard therapy?
If ctDNA is still detectable after you have completed standard treatments (for example, surgery, chemotherapy, radiation, and recommended endocrine or targeted therapy), it may suggest a higher risk that breast cancer cells remain in your body. In that situation, your care team might discuss options such as additional or intensified systemic therapy, closer monitoring, or participation in a clinical trial, depending on your stage, tumor subtype (such as hormone receptor or HER2 status), and overall health. If ctDNA is not detected, some patients may be followed with routine surveillance alone, but decisions are always individualized.
How is MRD testing different from mammograms, scans, or regular blood tests?
Standard breast cancer follow up usually includes physical exams, mammograms or other breast imaging, and sometimes additional scans or blood tests. These tests look for cancer that is large enough to detect by imaging or cause changes in organs or blood counts. MRD testing adds another layer by looking directly for tumor DNA in the blood, which in some cases can change weeks or months before something appears on imaging or causes symptoms. Routine blood tests check general health markers, while MRD tests are specifically designed to detect DNA changes related to breast cancer.
How does MRD testing work?
Most MRD tests in breast cancer are “personalized” or “tumor informed.” The lab starts by analyzing a sample of your breast tumor (from surgery or biopsy) to find the specific DNA changes that are unique to your cancer, then uses this information to create a custom blood test. Future blood draws are checked for those same DNA changes to see whether breast cancer DNA is still present or appears again over time.
Who might benefit from MRD testing?
MRD testing may be considered if you have finished treatment for early stage or locally advanced breast cancer and are in remission, particularly if your risk of recurrence is higher based on stage, lymph node involvement, or tumor subtype (such as triple negative or HER2 positive disease). It may also be explored in some people with metastatic breast cancer to help monitor how well systemic therapy is working, although this is still an emerging use and not standard everywhere.
What can MRD test results show?
MRD results generally fall into two main categories:
MRD negative: No breast cancer DNA is detected in your blood above the test’s limit at that time, which is generally reassuring and often linked with a lower risk of recurrence and improved prognosis.
MRD positive: Breast cancer DNA is found in your blood, which typically means cancer is still present or starting to return, even if scans look normal.
Your doctor will interpret these results in the context of your breast cancer type, stage, subtype, treatment history, and other tests.
How can MRD testing help guide treatment decisions?
MRD results can help your care team:
- Determine your initial prognosis.
- Detect possible recurrence earlier and consider starting or changing treatment sooner
- Track how well your current treatment is working and
- Decide whether to continue, change, or stop certain therapies, especially if MRD stays positive or becomes negative on repeated tests. In some situations, repeated MRD negative results may support avoiding unnecessary or prolonged treatment, which could reduce side effects and treatment burden, but de escalation strategies based on MRD alone are still being studied.
How often is MRD testing done?
MRD testing can be done at key time points—such as after completing curative intent treatment—and may be repeated every 2-3 months or at specific intervals during follow up if your team decides to use it. The exact schedule (or whether repeat testing is needed at all) depends on your diagnosis, treatment plan, the specific test being used, and your preferences.
Does a positive MRD result mean my cancer will definitely come back?
A positive MRD result suggests that cancer DNA is present and that there is a higher risk of recurrence, but it does not guarantee what will happen in the future. Your doctor may recommend closer monitoring, additional imaging, or changes to your treatment plan—such as adding or switching therapies or considering a clinical trial—based on this result and your overall risk profile.
Does a negative MRD result mean I am “cancer free”?
A negative MRD result means the test did not detect cancer DNA above its limit of detection at that time, which is reassuring, but no test is perfect. You will still need regular follow up visits, imaging, and other tests according to your care plan to watch for any changes over time.
What is the difference between a “tumor-informed” MRD test and a blood-based ctDNA test?
A “tumor-informed” MRD test and a blood-based ctDNA test are both blood tests that look for evidence of cancer in the bloodstream, but they are designed and used a bit differently.
In a tumor-informed MRD test, the lab starts by analyzing a sample of your tumor tissue (for example, from surgery or a biopsy). They look for the specific DNA changes (mutations) that are unique to your cancer. Then they create a personalized blood test that checks your blood for those exact changes over time. Because it is tailored to your tumor, this type of test can be very sensitive for finding very low levels of remaining cancer after treatment and for monitoring whether cancer might be coming back.
With a more general blood-based MRD test (sometimes called “tumor-naive” or “tumor-agnostic”), the lab does not use your tumor tissue to create a personalized test. Instead, the test looks in your blood for a panel of common cancer-related changes to the DNA. This can be useful when tumor tissue is unavailable, but it is less sensitive and specific than a tumor-informed test.
In simple terms:
- Tumor-informed MRD test = built “from your tumor up,” customized to your cancer, mainly used to look for minimal residual disease and recurrence.
- Blood-based MRD test = uses a standard panel to look for cancer-specific changes to the DNA in blood, without first studying your tumor.
Your oncology team can explain which test they are using, why it was chosen, and how to interpret the results in your specific situation.
Can MRD testing reduce “scanxiety” or worry about recurrence?
Many patients say MRD testing gives them more peace of mind by offering another way to check on their cancer status between visits, especially if results stay negative. For others, an early positive result can feel stressful but may also allow more time to plan and act with their care team if additional treatment is needed. Talking with your team about how you prefer to receive results and what they would mean can help you decide whether MRD testing is emotionally right for you.
Are MRD tests available for all cancer types?
Tumor informed MRD tests are being used and studied in several solid tumors, including breast, colorectal, and other cancers, but they are not yet routine for every patient or every cancer type. Availability and insurance coverage can vary by cancer type, stage, location, and health plan, so your oncologist can tell you whether a personalized MRD test is appropriate and accessible for your specific breast cancer diagnosis.
How do I talk to my doctor about MRD testing?
You can start by asking: “Is MRD or ctDNA testing available and appropriate for my type and stage of breast cancer?”, “What would we do differently based on a positive or negative result?”, and “How often would you recommend testing, and for how long?”. Your doctor can explain the potential benefits, limitations, cost and coverage issues, and whether a personalized MRD test fits into your overall care plan.
Is MRD testing a replacement for regular follow up care?
No. MRD testing is meant to complement—not replace—your regular follow up visits, imaging, blood work, and physical exams. It is one more tool your team can use to personalize your care and help you stay as informed and proactive as possible. This FAQ is for general education and is not a substitute for medical advice; always discuss your specific situation and test results with your oncology team.
What does it mean if my MRD result is “below the limit of detection” or the sample is “inadequate”?
Sometimes an MRD report will say that the amount of tumor DNA in your blood is below the test’s “limit of detection.” This means the test could not reliably measure any cancer DNA at or above the level it is designed to detect at that time. In many cases, this is treated similarly to a negative result and can be reassuring, but it does not prove with 100% certainty that there is no cancer anywhere in the body, so your doctor will still recommend routine follow‑up visits, labs, and scans.
In other situations, the report may say the sample was “inadequate” or “insufficient.” This usually means there was not enough usable DNA in the blood tube, the sample was delayed or mishandled in transit, or there was a technical issue in the lab that prevented a reliable result. An inadequate sample does not tell you anything about whether cancer is present or not. In that case, your care team may recommend repeating the blood draw, waiting until a better time (for example, when your blood counts have recovered), or relying on other tests and scans while deciding whether to try MRD testing again.
This FAQ is for general education and is not a substitute for medical advice. Always discuss your specific situation and test results with your oncology team.
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More Reading
MRD ctDNA Surveillance for Breast Cancer Recurrence
Learn How ctDNA Testing Can Help Inform Breast Cancer Management
ctDNA Treatment Response Assessment in Metastatic Invasive Lobular Carcinoma of the Breast
Blood Test May Help Predict Recurrence Risk for Early-Stage HR-Positive, HER2-Negative Breast Cancer
Prognosis and Circulating Tumor DNA Monitoring in Breast Cancer
Biomarkers: How Your Cancer’s Unique “Fingerprint” Can Guide Treatment
Advances in Genomic Testing- What You Need to Know
What is Precision Cancer Medicine?
FAQs: NGS-Genomic Testing and Cancer Care
| Other Resources: Natera Facing Recurrence Again? How MRD Testing Can Support You Every Step of the Way Signatera Results Patient Guide How to Prepare for Your Next MRD Test: Practical Tips and FAQs |
This educational resource was made possible by Natera, OmniOncology, and The Personalized Medicine Foundation.
References
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Goetz MP, Coombes RC, Page K, et al. The use of ctDNA MRD precision medicine surveillance after curative‑intent treatment for high‑risk breast cancer. Breast. 2024;74:102‑110.
Coombes RC, Page K, Salari R, et al. Personalized detection of circulating tumor DNA antedates breast cancer metastatic recurrence (EBLIS study). J Clin Oncol. 2019;37(19):1547‑1557.
McDonald ES, Tjan S, Smith IE, et al. Minimal residue disease detection in early‑stage breast cancer: current evidence and future directions for ctDNA‑based monitoring. Breast Cancer Res Treat. 2025;203(2):245‑259.
Radovich M, Jiang G, Hancock BA, et al. Personalized circulating tumor DNA for minimal residual disease detection and recurrence prediction in high‑risk early‑stage breast cancer (MSK‑LINC). J Clin Oncol. 2024;42(16)(suppl):3049.
