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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Oncology · HER2-Negative Breast Cancer

Decoding Your Pathology and Biomarker Report

At a Glance

HER2-negative breast cancer reports combine HER2, ER, PR, and Ki-67 results with tumor features and sometimes inherited BRCA testing. Together, these findings help explain hormone sensitivity, growth activity, family risk, and treatment options.

Your pathology report is the “blueprint” of your cancer. It contains the results of tests performed on a sample of your tumor tissue to identify specific proteins and genetic markers [1]. For HER2-negative breast cancer, these markers tell your doctor whether the cancer is fueled by hormones, how actively it is proliferating, and whether certain targeted therapies will work for you [2]. In addition to these biomarkers, your report will also detail invasive versus in-situ disease, histologic type, tumor size, grade (how abnormal the cells look), margins, and lymphovascular invasion.

Hormone Receptors (ER and PR)

The Estrogen Receptor (ER) and Progesterone Receptor (PR) tests look for “docking stations” on the cancer cells that allow hormones to fuel growth [3]. Remember that ER and PR are tested separately and are not interchangeable.

  • ER-Positive: Defined as staining in 1% to 100% of the tumor cells [3].
  • ER-Negative: Defined as less than 1% staining [3].
  • ER-Low Positive (1%–10%): This is a specific category for tumors that show only a small amount of estrogen receptor staining [3]. These tumors are heterogeneous; while they may receive less benefit from hormone therapy than strongly positive tumors, endocrine therapy is usually still offered. Biologically, they can sometimes have features closer to Triple-Negative Breast Cancer (TNBC) [4][5].

The HER2 Scoring System

To confirm your HER2-negative status, pathologists use a scale from 0 to 3+ [6]:

  • IHC 0: No staining is seen, or faint incomplete staining is seen in 10% or fewer of the tumor cells [6].
  • IHC 1+: Faint, incomplete staining is seen in more than 10% of cells [6].
  • IHC 2+: Weak-to-moderate complete staining is seen. This is an “in-between” result that requires a second test called FISH or ISH to look at the actual HER2 genes [1]. If the FISH test is negative, the cancer is confirmed as HER2-negative [7].
  • IHC 3+: Strong, complete staining, which means the cancer is HER2-positive.

Emerging Categories: HER2-Low and HER2-Ultralow

While these are not yet formal, standalone medical categories, they are increasingly important descriptors for choosing treatments [6].

  • HER2-Low: This refers to a score of IHC 1+, or IHC 2+ with a negative FISH test [6].
  • HER2-Ultralow: This refers to a score of IHC 0 where there is still a tiny amount of membrane staining visible under the microscope [8].

Identifying these subtle levels of HER2 is useful because newer drugs called antibody-drug conjugates (ADCs) have shown success in treating advanced or metastatic tumors with these low levels of the HER2 protein [8][7].

Ki-67: A Proliferation Marker

Ki-67 is a protein found in cells only when they are dividing. Your report will list a percentage (e.g., 20%), which represents how many cancer cells are actively proliferating [9].

  • High Ki-67: Generally means the cancer is growing more quickly.
  • Low Ki-67: Generally means the cancer is growing more slowly.

It is important to know that Ki-67 results can vary significantly between different laboratories or even different pathologists looking at the same slide [10][11]. Because of this variability, Ki-67 is a proliferation marker used as a “complement” to other information, not as a standalone test with a universally reliable cutoff to determine treatment [12][13].

Germline BRCA Testing

Beyond testing the tumor itself, your doctor may recommend testing you for inherited genetic mutations, specifically BRCA1 and BRCA2 [14]. This is usually done via a blood or saliva sample, often as part of a broader multigene panel [15].

This testing is crucial for HER2-negative patients for two reasons:

  1. Treatment Options: If you have a BRCA mutation, you may be eligible for a class of drugs called PARP inhibitors (such as olaparib or talazoparib) [16][17]. Eligibility for PARP inhibitors is not automatic; it depends on your stage, recurrence risk, and prior therapy.
  2. Family Risk: Finding a mutation can help your family members understand their own risk of developing breast, ovarian, or other cancers [14].

Current guidelines suggest offering this testing to most patients diagnosed at age 65 or younger, and to many older patients based on their family history or if they have metastatic disease [14][18].

Common questions in this guide

How is HER2-negative breast cancer confirmed on a pathology report?
A HER2 score of IHC 0 or 1+ is considered negative. An IHC 2+ result is an intermediate finding and usually needs FISH or ISH testing; if that test is negative, the cancer is classified as HER2-negative. IHC 3+ indicates HER2-positive disease.
What does an ER result between 1% and 10% mean?
This is called ER-low positive breast cancer, meaning a small proportion of tumor cells carry estrogen receptors. Endocrine therapy is usually offered, although the benefit may be smaller than in strongly ER-positive cancer and some features may resemble triple-negative breast cancer.
What are HER2-low and HER2-ultralow breast cancer?
HER2-low usually means IHC 1+ or IHC 2+ with a negative FISH or ISH test. HER2-ultralow describes IHC 0 with a tiny amount of membrane staining; these are treatment-related descriptions rather than fully separate diagnoses, and they may matter when considering antibody-drug conjugates for advanced or metastatic disease.
What does my Ki-67 percentage tell me?
Ki-67 estimates the percentage of cancer cells that are actively dividing, so a higher value generally suggests faster growth. Results can vary between laboratories and pathologists, so Ki-67 should be considered with the rest of the report rather than used alone to choose treatment.
Should I get inherited BRCA1 and BRCA2 testing?
Your doctor may recommend a blood or saliva test, often as part of a multigene panel. Testing is commonly offered to many patients diagnosed at age 65 or younger and to some older patients based on family history or metastatic disease; a mutation may affect PARP inhibitor eligibility and provide information for relatives.
Which parts of my pathology report should I review first?
Ask for a copy and look for whether the disease is invasive or in situ, tumor size, histologic type, grade, margins, lymphovascular invasion, and lymph node status. Also review the ER, PR, HER2, and Ki-67 results because they describe hormone sensitivity, HER2 status, and cell growth.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What were my exact percentages for ER and PR staining, and what was the intensity score?
  2. 2.Since my ER is between 1% and 10%, how does this change the way you view my cancer’s behavior compared to typical hormone-positive cancer?
  3. 3.What was my exact HER2 IHC score (0, 1+, or 2+), and if it was 2+, what were the FISH/ISH results?
  4. 4.Does my pathology report show any membrane staining that would qualify as 'HER2-ultralow,' and should we document that for future treatment options?
  5. 5.What is my Ki-67 percentage, and was it measured using the average counting method or the hotspot method?
  6. 6.Should I be referred for a multigene panel that includes germline BRCA1/2 testing based on my diagnosis and family history?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

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This page explains HER2-negative breast cancer pathology and biomarker results for education only and is not medical advice. Ask your oncologist, pathologist, or care team to interpret your report and discuss genetic testing or treatment.

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