HER2 Tumor Marker Test

Why this test may be ordered

• To determine if breast, stomach, or esophageal cancer is HER2 positive or negative
• To guide whether HER2 targeted therapy may be effective
• To assess how fast cancer may grow and likelihood of spread
• To test recurrent or metastatic cancer even if initial tumor was tested

Preparation and collection

Preparation depends on how your tissue sample will be taken. Ask your health care provider how to prepare. If you are getting medicine to relax or sleep during the procedure, you will probably need to fast for several hours before and have someone take you home.

A sample of tumor tissue is removed during a biopsy. Methods include a hollow needle inserted through your skin (fine needle aspiration or core needle biopsy), surgery (incisional or excisional biopsy), or endoscopy (using a scope to look inside your body).

Risks depend on how your tissue sample is taken. In general, if you are having a biopsy, you may have a little bruising or bleeding where the tissue was removed. Ask your provider to explain any risks from the test you're having.

Understanding results

HER2 test results are reported differently depending on the type of test you had. The main tests are IHC (immunohistochemistry), which measures the amount of HER2 protein on cancer cells, and FISH (fluorescence in situ hybridization), which checks for extra copies of the HER2 gene in cancer cells.

• IHC score 0 or 1+: Your cancer cells do not have too much HER2 protein. Your cancer is HER2 negative. Limitation: The test measures protein level; very low levels may still have some HER2 but not enough for targeted therapy. Next step: HER2 targeted therapy will not help. Discuss other treatment options with your provider.
• IHC score 2+: The amount of HER2 protein is borderline (equivocal). It is not clear if the cancer is HER2 positive or negative. Limitation: This result is inconclusive and requires further testing. Next step: You may need a different HER2 test, such as FISH, on the same or a new tissue sample to clarify the result.
• IHC score 3+: Your cancer cells have too much HER2 protein. Your cancer is HER2 positive. Limitation: A positive result indicates high likelihood of response to targeted therapy, but individual response may vary. Next step: HER2 targeted therapy is likely to help control your cancer. Discuss treatment options with your provider.
• FISH HER2 negative: You do not have too many HER2 genes in your cancer cells. Your cancer is HER2 negative. Limitation: This result is based on gene copies and provides additional confirmation. Next step: HER2 targeted therapy is unlikely to help your cancer. Discuss other treatment options with your provider.

• Blood tests for HER2 are not recommended because it is not clear how blood test results can plan cancer treatment.
• Cancer cells can change over time, so retesting may be needed for recurrent or metastatic disease even if the first tumor was tested.
• IHC score 2+ is borderline (equivocal) and requires additional testing, such as FISH, for a definitive result.

What to do next

Your healthcare provider will interpret your HER2 test results along with other factors to recommend a treatment plan. If your cancer is HER2 positive, targeted therapy may be an option. If HER2 negative, other treatments will be considered. For equivocal results, additional testing is needed.

• What type of HER2 test was performed on my sample (IHC or FISH)?
• What does my HER2 result mean for my cancer treatment options?
• If my result is equivocal, what additional tests are needed and how long will they take?
• Should I have my tumor retested if my cancer comes back or spreads?
• Are there any clinical trials for HER2-targeted therapies that I might be eligible for?

Evidence source

U.S. National Library of Medicine: HER2 Tumor Marker Test