Biomarker Resource Center
Breast Cancer Biomarkers
Reviewed by XpertPatient Medical Advisory · Updated August 2026 · Primary Source: cancer.gov
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What is a biomarker?
A biomarker is a signal your cancer leaves behind. Doctors find these signals in your blood or tumor tissue. The signals tell your doctor important things, like what type of cancer you have and how it is behaving.
Think of it like a clue. Your doctor collects clues from your biomarker test results. Those clues help build a picture of your cancer and help you have a more informed conversation with your doctor about next steps.
Everyone’s cancer is different, even people with the same type of cancer can have very different results. That is why biomarker testing matters. It helps your care team understand your cancer specifically.
For Breast Cancer
Why do biomarkers matter in breast cancer?
Two people can both have breast cancer, but their tumors can be very different. Biomarker tests help your doctor understand what is driving your specific cancer to grow. That information is an important part of the conversation you will have with your care team about next steps.
A good question to ask your doctor: Your biomarker results are an important piece of your overall picture. Ask your doctor to walk you through your ER, PR, and HER2 results and what they mean for you.
The most important breast cancer biomarkers are ER, PR, and HER2. Together they help your doctor understand what is driving your tumor to grow and which treatment approaches may be most appropriate for your situation.
Patient Poll
Have you had biomarker testing for your breast cancer?
The Tests Your Doctor May Order
Does your cancer use estrogen to grow?
ER stands for estrogen receptor. If your result is ER-positive, it means your tumor may use estrogen to grow. This is a common finding in breast cancer. Your doctor may talk with you about hormone-blocking options that are commonly used in this situation. Ask your doctor what an ER-positive result means for your specific case.
Does your cancer use progesterone to grow?
PR is similar to ER. A PR-positive result means the tumor may also respond to hormone-related approaches. Your doctor will look at ER and PR together. Ask your doctor what your PR result means alongside your other results.
Does your cancer make too much of a growth protein?
HER2 is a protein that can drive cancer growth when there is too much of it. HER2-positive is a common finding. Doctors commonly discuss specific options with patients who have this result. Talk to your doctor about what HER2-positive means for your situation.
How fast is your cancer growing?
Ki-67 measures how many cancer cells are dividing right now. A higher number means faster growth. A lower number means slower growth. Your doctor uses this information, along with your other results, to understand your cancer better. Ask your doctor what your Ki-67 number means for your care.
Did you inherit a gene that may affect your care?
BRCA1 and BRCA2 are genes that, when mutated, may increase cancer risk. This is an inherited result, meaning it came from your family. If you have a BRCA mutation, your doctor will talk with you about what options may be worth discussing. This result may also be relevant to close family members. Ask your doctor if BRCA testing is right for you.
Primary source: National Cancer Institute (cancer.gov) · Susan G. Komen · NCI · ARUP Consult
Watch & Learn
Important: This page is for education only. It is not medical advice. Every patient’s situation is different. Please talk to your doctor or care team about what your biomarker results mean for you specifically.
Common Questions
Breast Cancer Biomarkers, Your Questions Answered
What does ER-positive mean?
ER-positive means your tumor may use estrogen to grow. Doctors commonly discuss hormone-related approaches with patients who have this result. Talk to your doctor about what ER-positive means for you specifically and what options may be worth exploring.
What is HER2-positive breast cancer?
HER2-positive means your tumor makes too much of a growth protein called HER2. This is a well-known finding that doctors have experience managing. Ask your doctor what HER2-positive means for your care and what approaches are commonly used.
What is triple-negative breast cancer?
Triple-negative means your cancer tested negative for ER, PR, and HER2. This is a specific subtype of breast cancer with its own set of approaches that doctors commonly discuss with patients. Talk to your doctor about what triple-negative means for your situation.
Should I ask about BRCA testing?
If you have a family history of breast or ovarian cancer, or if you were diagnosed at a younger age, it is worth asking your doctor whether BRCA testing makes sense for you. Your doctor can help you decide if it is right for your situation.
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From the Breast Cancer Center on XpertPatient
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