Medical Oncologist
Your report explained
HER2-low: a result that did not exist a few years ago
HER2-low means your tumour carries a small amount of the HER2 protein, more than none but not enough to be called HER2 positive. These cancers used to be filed simply as HER2 negative. The band is now named separately because one newer treatment can work in it. This page explains the scores and what the result changes for you.
MM
Medically reviewed by Dr. Muralidhar MuddusettyConsultant Surgical Oncologist · MBBS (AIIMS), MS (Surgery, AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh) · last reviewed September 2026, next review due September 2027
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The short answer
What does HER2-low mean on my report?
HER2-low means your tumour carries a small amount of the HER2 protein. Not enough to be called HER2 positive, but more than none. Until recently these cancers were simply filed as HER2 negative. They are now named separately because a treatment exists that can work in this group.
Where the word comes from
HER2 is a protein on the surface of cells that tells them to grow. The laboratory stains the tumour tissue for it and scores how strongly it shows up. A strong result means HER2 positive. No staining at all means HER2 negative. The faint results in between are what HER2-low describes.
Why it was not a category before
The older HER2 drugs only work when there is a great deal of the protein to attach to, so a faint result changed nothing and there was no reason to name it. A newer kind of drug carries chemotherapy directly to any cell showing even a little HER2, and that is what made the middle band worth reporting.
If your report predates this change, the faint result may simply be recorded as negative. Ask for the staining score itself.On your report
The scores, and what each one is called
- IHC 0
- No staining seen. This is HER2 negative in the older and the newer sense, and is sometimes now written as HER2 ultralow if the faintest trace is present.
- IHC 1+
- Faint staining. This falls in the HER2-low band.
- IHC 2+
- Moderate staining. A further test on the genes themselves decides which side it falls on. If that test is negative, it is HER2-low.
- IHC 3+
- Strong staining. This is HER2 positive, and the established HER2 treatments apply.
- FISH, or ISH
- The follow-up test used when the staining is moderate. It counts copies of the HER2 gene rather than looking at the protein.
- Immunohistochemistry, or IHC
- The staining test itself, done on your tumour tissue.
Not sure whether this applies to you?
Ask an oncologistWhat it changes
What HER2-low actually changes for you
Less than most people expect at diagnosis, and more than most people expect later.
It does not change your subtype
Your cancer is still classified by its hormone receptors. HER2-low and hormone positive is treated as a hormone sensitive cancer. HER2-low and hormone negative is still treated as triple negative.
It does not change early treatment
Surgery, radiotherapy and the usual decisions about chemotherapy and hormone tablets are made the same way. Nothing about your first treatment plan turns on this result.
This is the part families most often misread.It matters if the cancer returns or spreads
In cancer that has spread, HER2-low opens a treatment option that would not otherwise be available. This is the situation the category was created for.
It is worth knowing and recording
Even if it changes nothing today, having the score written in your file means the option is not overlooked years later.
Worth asking for
- The exact IHC score, not just positive or negative
- Whether a gene test was needed
- A copy of the report for your own file
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Side by side
How the three HER2 groups differ
What the report shows
What it means in practice
HER2 positive, a strong staining result
Established HER2 treatments are part of the plan from the start
HER2-low, a faint or moderate result without gene change
Treated as HER2 negative now; an extra option exists if it spreads
HER2 negative, no staining at all
HER2 plays no part in the plan
Moderate staining awaiting a gene test
The result is genuinely not known yet. Wait for it before deciding
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Being straight with you
What this result cannot tell you
HER2-low does not tell you that your cancer is more or less serious than a HER2 negative one. On the evidence so far, cancers in this band behave much like the negative ones they used to be grouped with.
The category is still settling
Pathologists find the faintest scores the hardest to agree on, and two laboratories can report the same tissue differently. Work is still going on to make the reading more consistent. Your oncologist knows this, which is why the result is used to open an option rather than to drive your whole plan.
It is not a reason to change your current treatment
People read about a new drug and ask to switch to it. The treatment this result unlocks is for cancer that has spread, and it is given in a particular order after other treatments. Asking to move it earlier is not in your interest.
What to do with it
Write the score down and keep the report. Ask your oncologist to confirm which band you are in, whether it changes anything now, and whether it would change anything later. Those three answers are the whole practical value of this line today.
Commonly believed
What people assume when they read HER2-low
HER2-low is a new and more dangerous kind of cancer.
It is a new label, not a new disease. These cancers were being diagnosed and treated all along, filed under HER2 negative. Naming the group changed what can be offered later, not how the cancer behaves.
I should be on HER2 treatment because I am HER2-low.
The older HER2 drugs need a large amount of the protein to work and do not help in this band. The newer drug that does work here is used for cancer that has spread. Being HER2-low in early breast cancer does not add a drug to your plan.
My old report says negative, so the doctors got it wrong.
Older reports predate the category and recorded faint staining as negative, which was correct practice at the time. The original slides can usually be re-read if the result would change a decision. Ask rather than assume an error.
Being HER2-low means chemotherapy can be avoided.
It has no bearing on that decision. Whether chemotherapy is offered depends on your hormone receptors, the grade, the size and the node result, and sometimes on a gene test. HER2-low does not enter that calculation.
Questions we are asked
Common questions about HER2-low
Am I HER2 positive or HER2 negative?
For treatment purposes today you are HER2 negative. HER2-low sits inside the negative group and is reported separately because it opens one option if the cancer ever spreads. Your subtype is still named by your hormone receptors.
My report says HER2 1+. Is that HER2-low?
Yes. Faint staining falls in the HER2-low band. A moderate result also counts as low, but only after a further gene test comes back negative. If your report shows a moderate result with no gene test, ask whether one was done.
Does HER2-low change my chances?
On the evidence so far it does not meaningfully change how the cancer behaves compared with HER2 negative disease. What it changes is the list of treatments available if the cancer comes back or spreads. Read it as an extra option, not as a new risk.
Should I ask for my tissue to be retested?
It is worth asking if your report is older and records only positive or negative, and if knowing the score would change a decision you face now. If your treatment is settled and the cancer has not spread, retesting usually changes nothing today.
Can the HER2 result change over time?
It can differ between the original tumour and a later recurrence, which is why a fresh biopsy is often taken if the cancer returns. It does not drift while the same tumour sits untreated, so repeat testing during your current treatment is not needed.
Is HER2-low the same as triple negative?
They describe different things. Triple negative means no hormone receptors and no HER2. A cancer can be triple negative and also HER2-low, which is precisely the group for whom the new option matters most. Ask which combination applies to you.
Why do two laboratories report it differently?
Because the faintest scores are a judgement made by eye, and tissue handling affects staining. This is a known weakness of the category and work to standardise it is ongoing. Where the result drives a real decision, a review of the slides is reasonable.
What is HER2 ultralow?
A further band some laboratories now report for the very faintest trace of staining, below the low band. It is newer still and not every centre reports it. Ask your oncologist whether it appears on your report and whether it changes anything for you.
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Sources
- Cancer Research UK — HER2 status and breast cancer
- National Cancer Institute — HER2 (human epidermal growth factor receptor 2)
- Breast Cancer Now — HER2 status explained
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.