What a HER2 IHC score of 2+ means

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 intrinsically a cancer thing.

The problem is quantity. Some types of cancer cells make larger than normal amounts of HER2, including certain cancers of the breast, stomach and oesophagus. 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 hybridisation, 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 usual order and the reason for it: usually a protein test is done first because those tests are faster and less expensive.

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

0 or 1+ — your cancer is HER2 negative and will not respond to HER2 targeted therapy.

3+ — your cancer is HER2 positive and is likely to respond to HER2 targeted therapy.

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 tumour 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.

MedlinePlus describes the logistics: the test may be done on the same tissue sample, or you may need to provide a new sample. Which of those applies depends on how much usable tissue is left from the original biopsy, so it is worth asking rather than assuming.

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, MedlinePlus says HER2 targeted therapy is likely to help your cancer.

If it comes back negative, MedlinePlus says your provider will discuss other treatment options. That is not a dead end — it means 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 are allowed to do so without needing 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.