What a HER2 IHC score of 2+ means

This page is for people whose pathology report includes a HER2 IHC score. It explains what HER2 is, what each score means, and what happens after a borderline 2+ result.

HER2 stands for human epidermal growth factor receptor 2. MedlinePlus describes it as a protein involved in normal cell growth — meaning healthy cells have it too, and it is not a cancer protein by nature.

The problem is quantity. Some types of cancer cells make larger than normal amounts of HER2, including certain cancers of the breast, stomach and esophagus. MedlinePlus notes that cancers with elevated HER2 tend to grow quickly and spread, but that targeted therapy can block these proteins to help control the disease.

That is the reason anyone measures it. The number is there to decide whether a particular class of drug belongs in your plan.

There are two main ways to check HER2, and they do not measure the same thing.

• IHC, or immunohistochemistry, measures the amount of HER2 protein on cancer cell surfaces.
• FISH, or fluorescence in situ hybridization, checks for extra copies of the HER2 gene in cancer cells.

One counts protein on the outside of the cell. The other counts gene copies inside it.

MedlinePlus explains the order and the reason for it: for some cancers, an IHC test is often done first because it is faster and less expensive.

IHC results come back as 0, 1+, 2+ or 3+. MedlinePlus sets out what each end means.

0 or 1+ — the result is called HER2 negative.

3+ — the cancer cells have high levels of HER2 protein, and the result is called HER2 positive.

2+ — the amount of HER2 protein is borderline, and the test result is not clear. MedlinePlus adds that you may need to have a different type of HER2 tumor marker test.

A 2+ is not a middling diagnosis. It is an unfinished sentence.

The point of the follow-up test is to break the tie by asking the gene question instead of the protein question.

The follow-up test needs tissue. Whether it uses your existing sample or a new one is something to ask your team, since MedlinePlus notes a new sample may be recommended in some situations, such as metastatic or recurrent cancer.

The wait is the hard part. You have already had one round of uncertainty and now there is another. It is reasonable to ask how long the second test takes and whether anything in your treatment plan is on hold while it runs.

If the follow-up confirms HER2 positive, ask your team whether HER2 targeted therapy fits your plan.

If it comes back negative, ask your team what other treatment options apply. That is not a dead end — the plan is built around something other than HER2.

Either way, the value of resolving a 2+ is that it removes a guess from your treatment decisions. Nobody wants to give or withhold a drug on the basis of a borderline stain.

Pathology reports are written for clinicians, and HER2 sections are especially dense — scores, staining percentages, ratios, assay names. If you are looking at yours before your appointment, you do not have to decode it alone.

Write down the exact wording that confused you and bring it with you. "My report says 2+, what does that mean for me?" is a completely standard question, and the answer should be specific to your sample, your cancer type and what test is happening next.