Understanding Your Breast Cancer Test Results: ER, PR and HER2 Explained

After a breast biopsy confirms cancer, the pathology report provides important information about the cancer cells. Three results you are likely to see are ER, PR and HER2.

These abbreviations describe characteristics of the cancer that help doctors understand what may be helping it grow and, importantly, which treatments may be effective.

ER, PR and HER2 do not determine the stage of breast cancer by themselves. Doctors consider them together with the tumor size, lymph-node involvement, whether the cancer has spread, tumor grade and other findings.

 

Key Takeaways

• ER means estrogen receptor and PR means progesterone receptor.
• ER and PR show whether hormones may be helping the cancer grow.
• HER2 means human epidermal growth factor receptor 2, a protein involved in cell growth.
• ER- or PR-positive cancers may respond to hormone therapy.
• HER2-positive cancers may respond to HER2-targeted treatment.
• HER2-low and HER2-ultralow results may also influence treatment for some patients with advanced breast cancer.
• Doctors interpret these results together with the cancer's stage, grade and other findings.

 

What does ER mean?

ER stands for estrogen receptor.
Some breast cancer cells have receptors that estrogen can attach to. When this happens, estrogen may encourage the cancer cells to grow.

If these receptors are present, the cancer is called ER-positive (ER+). If they are not present, it is described as ER-negative (ER−).

Your pathology report may also show the percentage of cancer cells that are ER-positive. Under current guidelines, staining in at least 1% of tumor cells is considered positive.
Results between 1% and 10% may be described as ER low positive.

 

What does PR mean?

PR stands for progesterone receptor.
Progesterone is another hormone that can influence the growth of some breast cancers.
If progesterone receptors are found, the cancer is called PR-positive (PR+). If they are not detected, it is called PR-negative (PR−).
Doctors commonly look at ER and PR together. Cancer that is positive for ER, PR or both may be described as hormone receptor-positive, or HR-positive.

 

Why do ER and PR results matter?

If breast cancer is hormone receptor-positive, it may respond to endocrine therapy, also called hormone therapy.
These medicines work by blocking the effect of estrogen on cancer cells or reducing the amount of estrogen available in the body.
The treatment recommended depends on factors such as your age, whether you have reached menopause, the cancer stage and other characteristics of the tumor.

 

What does HER2 mean?

HER2 stands for human epidermal growth factor receptor 2.
HER2 is a protein found on the surface of cells and helps regulate cell growth. Some breast cancers have unusually high levels of HER2 or extra copies of the HER2 gene, which can send stronger signals for cancer cells to grow.
These cancers are called HER2-positive.
Knowing HER2 status is important because medicines are available that specifically target this protein. These are known as HER2-targeted therapies.
 
 

How is HER2 tested?

HER2 is commonly assessed using immunohistochemistry, or IHC, which measures HER2 protein on the cancer cells.

HER2 result	What it generally means
IHC 0	No or very little HER2 detected
IHC 1+	Low HER2 expression; traditionally considered HER2-negative
IHC 2+	Borderline result; another test is usually needed
IHC 3+	HER2-positive

 
If the result is IHC 2+, another test is usually performed to look more closely at the HER2 gene. This is called in situ hybridization (ISH). Different types of ISH can be used, including FISH (fluorescence in situ hybridization) and DISH (dual in situ hybridization). At Bumrungrad International Hospital, DISH is used.
These tests show whether the HER2 gene has extra copies and help determine whether the cancer is HER2-positive.
 
 

What are HER2-low and HER2-ultralow breast cancer?

Breast cancer is no longer discussed only as HER2-positive or HER2-negative. You may now also hear the terms HER2-low and HER2-ultralow.
These cancers are not the same as HER2-positive breast cancer. They have smaller amounts of HER2 on the cancer cells.
HER2-low generally includes cancers with an IHC result of 1+, or 2+ with a negative ISH test.
HER2-ultralow refers to certain cancers reported as IHC 0 in which very faint HER2 staining can still be detected.
These distinctions have become important because newer medicines may be able to target even small amounts of HER2. Some patients with advanced HER2-low or HER2-ultralow breast cancer may therefore have additional treatment options.
Your oncologist will interpret these results together with your hormone receptor status, cancer stage and previous treatments.
 
 

What do ER, PR and HER2 results mean together?

Doctors look at all three results together because their combination helps explain the biology of the cancer and guides treatment.
 

Test result	What it may mean
ER and/or PR positive, HER2 negative	Hormone therapy may be important
ER and/or PR positive, HER2 positive	Hormone therapy and HER2-targeted treatment may both be considered
ER and PR negative, HER2 positive	HER2-targeted treatment may be important
ER negative, PR negative and HER2 negative	Called triple-negative breast cancer. Because ER, PR and HER2 are not available as treatment targets, hormone therapy and conventional HER2-targeted treatment are generally not used. Chemotherapy, immunotherapy or certain targeted medicines may still be options, depending on the cancer stage, biomarkers and genetic findings.

 
 

Breast cancer care at Bumrungrad

At Bumrungrad International Hospital:

• The Breast Center works closely with the Horizon Regional Cancer Center, pathologists, radiologists and other specialists.
• Bumrungrad Laboratory has maintained College of American Pathologists (CAP) accreditation since 2016. CAP accreditation reflects rigorous standards for laboratory quality, accuracy and performance.
• Bumrungrad's laboratory capabilities include complex testing such as DNA sequencing.
• ER, PR and HER2 results are considered together with the cancer's stage, grade and other findings to guide treatment.
• Treatment may include hormone therapy, targeted therapy, chemotherapy, surgery or radiation therapy.
• 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

Does ER-positive mean estrogen caused my breast cancer?
No. ER-positive means the cancer cells have estrogen receptors and may use estrogen as a signal to grow. It does not mean that estrogen alone caused the cancer.
 
Is HER2-positive breast cancer worse?
HER2-positive cancers may grow more aggressively than some other breast cancers. However, HER2-targeted medicines have significantly changed treatment. Outlook depends on the stage of the cancer, other tumor characteristics and how well it responds to therapy.
 
What does triple-negative breast cancer mean?
Triple-negative breast cancer means the cancer is negative for ER, PR and HER2.
This means hormone therapy and conventional HER2-targeted medicines are generally not effective, but triple-negative does not mean untreatable. Chemotherapy, immunotherapy and certain targeted medicines may still be options.
 
Can ER, PR or HER2 results change?
Yes. These markers can sometimes change if breast cancer returns or spreads to another part of the body. Doctors may therefore recommend another biopsy and repeat testing when the result could influence treatment.
 
Understanding ER, PR and HER2 can make a complicated pathology report easier to interpret. These results do not tell the whole story, but they provide important clues about how the cancer behaves and which treatments may work best.
 


Medical references

1. Allison KH, Hammond MEH, Dowsett M, et al. Estrogen and Progesterone Receptor Testing in Breast Cancer: ASCO/CAP Guideline Update. Journal of Clinical Oncology. 2020;38(12):1346–1366.
2. Wolff AC, Somerfield MR, Dowsett M, et al. Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: ASCO–College of American Pathologists Guideline Update. Journal of Clinical Oncology. 2023;41(22):3867–3872.
3. National Cancer Institute. Breast Cancer Biomarkers: Hormone Receptors, HER2, and Others.
4. Modi S, Jacot W, Yamashita T, et al. Trastuzumab Deruxtecan in Previously Treated HER2-Low Advanced Breast Cancer. New England Journal of Medicine. 2022;387(1):9–20.
5. Bardia A, Hu X, Dent R, et al. Trastuzumab Deruxtecan after Endocrine Therapy in Metastatic Breast Cancer. New England Journal of Medicine. 2024;391(22):2110–2122.
6. U.S. Food and Drug Administration. FDA Approves Fam-Trastuzumab Deruxtecan-nxki for Unresectable or Metastatic HR-Positive, HER2-Low or HER2-Ultralow Breast Cancer. 2025.
7. College of American Pathologists. Laboratory Accreditation Program.

 


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