The short answer
ER and PR status tell whether breast cancer cells have receptors for the hormones estrogen and progesterone. Positive results mean hormone therapy may help.
ER means estrogen receptor; PR means progesterone receptor.
These receptors are found on some breast cancer cells.
'Positive' means the cells have the receptors and may respond to hormone therapy.
'Negative' means the cells lack them, so hormone therapy is less likely to help.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
What the letters mean
This page is for anyone with breast cancer whose pathology report lists ER and PR status. It explains what the results mean, how they guide treatment, and what they do not tell you.
ER stands for estrogen receptor. PR stands for progesterone receptor. Both are proteins found on some breast cancer cells. Receptors act like docking stations. When the hormones estrogen or progesterone attach to these stations, they can signal the cell to grow.
A pathologist (a doctor who studies tissue under a microscope) tests your breast cancer tissue for both receptors. The test uses a stain called immunohistochemistry, or IHC. The result tells your care team whether these hormones are likely fueling your cancer.
Reading positive and negative, including "low positive"
A positive result means the cancer cells carry these receptors. This is reported as a percentage, from 0% to 100% of cells staining. Staining in 10% or more of cells is usually called clearly positive. A negative result means fewer than 1% of cells stain. The cancer has essentially none of these receptors.
Between those two, there is a middle category. Current guidelines from ASCO and the College of American Pathologists call it "ER-low positive." It covers staining in roughly 1% to 10% of cells. This group can behave somewhat differently than clearly positive or clearly negative cancers. Your oncologist may discuss it specifically if it applies to you.
Why it guides treatment
ER and PR status is one of the most useful parts of a breast cancer report. It points directly at whether hormone therapy is likely to help. Hormone therapy works by blocking estrogen, lowering estrogen levels, or blocking the receptor itself. If cells carry the receptor, this approach can meaningfully lower the chance the cancer returns. If they do not, hormone therapy is not expected to work. There is no receptor for the drug to act on.
Most breast cancers are hormone-receptor positive. That is one reason hormone therapy is such a common part of treatment.
The bigger biomarker panel
ER and PR are almost always tested together with a third marker, HER2. When all three come back negative, the cancer is called triple-negative. It is treated with different approaches, mainly chemotherapy, and in some cases immunotherapy. Your pathology report should list ER, PR, and HER2 together. They are read as one panel, not separately.
What it does not tell you
Receptor status does not tell you the stage of your cancer. That means its size, and whether it has spread. It also does not guarantee how well hormone therapy will work for you. It identifies who is a reasonable candidate, not a guaranteed responder. Receptor status can also change over time, as explained below.
Is this urgent?
ER and PR testing is routine and expected. It is not an emergency finding on its own. What matters is making sure results are ready before treatment planning begins, since they shape which drugs are offered.
How the test is actually scored
A pathologist looks at your tumor sample under a microscope after IHC staining. They count what fraction of the cancer cell nuclei (the cell's control centers) show brown staining for each receptor. Some labs also note how strong the staining looks, not just how many cells stain. Exact percentages can vary a little between labs. That is why the ASCO/CAP guideline asks laboratories to have a set procedure for confirming results when staining is low. It is also one reason your care team looks at the overall pattern rather than treating a single percentage point as an exact cutoff.
Why testing happens more than once for some people
ER and PR are usually tested once, on your original tumor sample. But if your cancer returns years later, doctors sometimes repeat the test on the new tissue, since receptor status can change between the original tumor and a recurrence. A change from positive to negative, or the reverse, is uncommon but does happen. When it does, it can shift which treatments make sense. If you are facing a recurrence, ask whether repeat receptor testing is being done on the new tissue rather than relying on your original result alone.
What to ask your team
- What were my exact ER and PR percentages, not just positive or negative?
- Am I in the "ER-low positive" category, and does that change my options?
- What does this mean for hormone therapy specifically?
- How do these results fit with my HER2 status?
Sources
Common questions
What are ER and PR?
They are receptors — docking points — on some breast cancer cells for the hormones estrogen (ER) and progesterone (PR). Their presence affects how the cancer may be treated.
What does ER-positive mean?
It means the cancer cells have estrogen receptors, so estrogen can encourage them to grow. These cancers often respond to hormone therapy that blocks or lowers estrogen.
Is ER-positive or ER-negative better?
ER-positive cancers can be treated with hormone therapy, which is an advantage. Outlook depends on many factors, so no single result defines it.
How is this related to HER2 and triple-negative?
ER, PR, and HER2 are tested together. When all three are negative, the cancer is called triple-negative, which is treated differently.
Your next step
Plain-language definitions for the words on your report.
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Written by: Cancer ExplainedSources last checked: 2026-07-14 what this meansLast updated: 2026-08-18Next planned review: 2027-07-14
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education. Low-risk educational or organizational content. Medical facts are cited to authoritative sources.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.