HER2 Tumor Marker Test Test

The HER2 tumor marker test checks if your cancer has high levels of a protein called HER2, which helps doctors decide if targeted therapy will work for you.

What this test measures

This test measures either the amount of HER2 protein on cancer cells or the number of copies of the HER2 gene inside cancer cells. It helps determine if a cancer is HER2 positive or negative.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

A high result (IHC 3+ or FISH positive) means your cancer is HER2 positive and likely to respond to HER2 targeted therapy.

Lower-than-normal results

A low result (IHC 0 or 1+, or FISH negative) means your cancer is HER2 negative and will not respond to HER2 targeted therapy.

Frequently asked questions

What does HER2 stand for?

HER2 stands for human epidermal growth factor receptor 2. It is also called HER2/neu.

How is the HER2 test done?

The test usually uses a sample of tumor tissue to measure either the amount of HER2 protein or the number of HER2 gene copies.

What does an IHC score of 2+ mean?

A score of 2+ means the amount of HER2 protein is borderline (equivocal). You may need another test to get a clear result.

Can a blood test be used for HER2 testing?

Blood tests to measure HER2 are usually not recommended because it is not clear how the results can plan cancer treatment.

What cancers are HER2 testing used for?

HER2 testing is mainly used for cancers of the breast, stomach, esophagus, ovaries, bladder, and pancreas.

Sources

MedlinePlus: HER2 Tumor Marker Test — NIH MedlinePlus

Last updated July 7, 2026. Information is aggregated from official public sources and is not a substitute for professional medical care.