What is HER2 testing for breast cancer

Q: What is HER2 testing for breast cancer

HER2 stands for human epidermal growth factor receptor 2. It's a protein found on the surface of breast cancer cells. Think of it like a growth signal receiver—when HER2 is present in high amounts, it can send signals that tell cancer cells to grow and divide faster. Everyone has HER2 genes, but in some breast cancers, there are too many copies of the HER2 gene, or the protein is overproduced. This is called HER2-positive HER2+ breast cancer. When HER2 levels are normal or low, it's called HER2-

Breast CancerDecember 1, 2025Navis AI

For informational purposes only

This answer was generated by AI grounded in NCCN guidelines and published medical literature. It is not medical advice. Always consult your oncologist or care team before making treatment decisions.

HER2 Testing for Breast Cancer: What You Need to Know

What is HER2?

HER2 stands for human epidermal growth factor receptor 2. It's a protein found on the surface of breast cancer cells. Think of it like a growth signal receiver—when HER2 is present in high amounts, it can send signals that tell cancer cells to grow and divide faster.

Everyone has HER2 genes, but in some breast cancers, there are too many copies of the HER2 gene, or the protein is overproduced. This is called HER2-positive (HER2+) breast cancer. When HER2 levels are normal or low, it's called HER2-negative (HER2-).

Why Doctors Test for HER2

According to the NCCN Guidelines for Patients: Metastatic Breast Cancer (2024), HER2 testing is a standard part of breast cancer diagnosis because:

It guides treatment decisions – HER2 status helps determine which therapies might work best for your specific cancer
It affects prognosis – HER2 status is part of how doctors stage and predict the course of your cancer
It identifies targeted therapy options – If you're HER2-positive, you may be eligible for HER2-targeted therapies, which are drugs designed specifically to attack HER2-positive cancer cells

How HER2 Testing Works

HER2 testing is performed on a tissue sample from your biopsy. According to the NCCN guidelines, doctors typically use one or more of these methods:

Immunohistochemistry (IHC) – A lab test that uses special stains to detect HER2 protein on cancer cells
In situ hybridization (ISH) – A lab test that counts the number of HER2 genes in cancer cells
Combination testing – Sometimes both methods are used to get the most accurate result

What the Results Mean

HER2-positive – High levels of HER2 protein or extra HER2 genes are present
HER2-negative – Normal or low levels of HER2
HER2 equivocal – Results are unclear and may require additional testing

Questions to Ask Your Care Team

Since HER2 status is important for your treatment plan, consider asking:

What is my HER2 status, and what does this mean for my treatment options?
Will my HER2 status affect which therapies I'm eligible for?
If I'm HER2-positive, am I a candidate for HER2-targeted therapy?
Will my HER2 status be tested again during or after treatment?
How does my HER2 status compare with my hormone receptor status in terms of treatment planning?

Important Context

According to the NCCN Guidelines for Patients: Inflammatory Breast Cancer (2025), HER2 testing is particularly important because inflammatory breast cancer can vary in its HER2 expression—meaning some inflammatory breast cancers are HER2-positive and others are HER2-negative. This variation means your specific HER2 result is crucial for personalizing your treatment plan.

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.

This is general information.

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