Medical Oncologist
Trastuzumab eligibility
Who Can Take — Trastuzumab?
Trastuzumab is prescribed only when your tumour tests HER2-positive. Without that confirmed result, the treatment is not expected to help. Testing your biopsy sample is the first step — not an optional one.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- HER2 testing decides it — A laboratory result from your biopsy, not your cancer type alone, determines whether trastuzumab is right for you.
- A minority of cancers qualify — HER2-positive tumours are a subset of breast and gastric cancers. Testing shows which group you are in.
- Borderline results need a second test — An intermediate IHC score leads to a more detailed gene-level test before any decision is made.
- Heart function is assessed first — Trastuzumab can affect heart muscle over time, so a baseline heart check is part of the eligibility assessment.
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Trastuzumab is for people whose cancer tests HER2-positive. Eligibility is confirmed by laboratory testing of your tumour tissue — not assumed from your cancer type alone. It is used in HER2-positive breast, stomach and gastro-oesophageal junction cancers. Your oncologist decides after reviewing your biopsy result and overall health.
What do all these test results mean?
- HER2
- A protein found on the surface of some cancer cells. When a tumour produces too much HER2, it tends to grow more quickly. Trastuzumab is designed to attach to this protein and interfere with that process.
- IHC (immunohistochemistry)
- The standard first test done on your tumour tissue. It gives a score of 0, 1+, 2+, or 3+. A score of 3+ confirms HER2-positive. Scores of 0 or 1+ mean HER2-negative.
- FISH or SISH
- A gene-level test used when the IHC score is 2+, which is borderline. It checks whether the HER2 gene is amplified in your tumour cells. A positive result confirms HER2-positive.
- HER2-positive
- Your tumour is overproducing the HER2 protein. This is the group for whom trastuzumab is recommended by NCCN, ASCO and ESMO as part of standard treatment.
- HER2-negative
- Your tumour is not overproducing HER2. Trastuzumab is not indicated. Your oncologist will recommend a treatment the evidence supports for your specific result.
- HER2-low
- A score of 1+ or a weakly positive 2+ without gene amplification. Not eligible for trastuzumab, but this group may be considered for other HER2-directed medicines — a separate clinical question to raise with your oncologist.
Are you likely eligible for trastuzumab?
- Your tumour biopsy has confirmed HER2-positive status — IHC 3+, or IHC 2+ with a positive FISH or SISH test
- Your cancer is breast cancer, stomach cancer, or cancer of the gastro-oesophageal junction
- Your heart function has been assessed and is suitable for treatment
- Your kidney and liver function are adequate, confirmed by blood tests before you start
- Your oncologist has reviewed your full results and is recommending trastuzumab as part of your plan
What testing confirms you are eligible?
Eligibility is established from your tumour biopsy — usually the one already taken at diagnosis. The laboratory does not need a new procedure in most cases.
The first test is IHC, which scores HER2 protein expression from 0 to 3+. A score of 3+ confirms HER2-positive and is enough to proceed. A score of 2+ is borderline, so a second test — FISH or SISH — is then done to check whether the HER2 gene is amplified in your tumour cells.
Results generally take one to two weeks. If the original biopsy sample is too small or unsuitable, a repeat biopsy may be needed before the question can be answered.
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What happens if your tumour is not HER2-positive?
Being HER2-negative or HER2-low means trastuzumab is not indicated for you. This reflects the biology of your tumour — it is not a statement about how serious your cancer is.
Your oncologist will recommend a treatment the evidence supports for your specific result — which may be chemotherapy, hormone therapy, targeted therapy, or a combination.
If your cancer recurs or spreads to a new site, HER2 status can sometimes be re-tested, because tumours can change. Ask your team whether repeat testing is relevant to your situation.
Questions families ask most
Can we request trastuzumab even if the IHC result is negative?
Trastuzumab is not expected to benefit tumours that do not overexpress HER2, and it carries real risks — including effects on heart function — that are not worth taking without a reasonable prospect of benefit. Your oncologist will not recommend it without a confirmed positive result. If you want certainty about the test, you can ask for the result in writing and request a second opinion on the interpretation. That is a reasonable and entirely appropriate thing to do.
Does a negative result mean the cancer is more serious?
No. HER2 status is about the molecular biology of the tumour, not about how advanced the disease is. HER2-negative tumours are not more dangerous than HER2-positive ones — they simply do not have the protein that trastuzumab targets. Being HER2-negative means a different treatment pathway, not a worse outlook. Your oncologist can explain what the evidence says for your specific cancer type and result.
Will my heart be checked before I start?
Yes. Trastuzumab can affect heart muscle function in some people over the course of treatment. Before you start, your team will assess your heart — usually with an echocardiogram or a MUGA scan. Heart function is then rechecked at regular intervals during treatment. If your heart function changes significantly, treatment may be paused or adjusted. Tell your team about any existing heart condition before you begin.
Can trastuzumab be used alongside chemotherapy?
Yes, and for many HER2-positive cancers, combining trastuzumab with chemotherapy is the standard approach rather than using it alone. Whether a combination applies to you depends on your cancer type, stage and overall fitness. Your oncologist will explain which regimen is being recommended for your situation and what each part of the treatment is intended to do.
What if the HER2 result was borderline — IHC 2+?
An IHC score of 2+ is not a final answer. It means a second, more precise test — FISH or SISH — is needed before your team can make a decision. A positive FISH or SISH result confirms HER2-positive and means trastuzumab may be indicated. A negative result means the tumour is HER2-low and trastuzumab would not be recommended. Ask your team whether your 2+ result has already had confirmatory testing, and what the outcome was.
Can HER2 status change over time?
It can, particularly if a cancer recurs or spreads to a new site. The tumour at the new site may have different characteristics from the original. This is why re-biopsy and re-testing are sometimes recommended when the disease changes, rather than relying on a result from years earlier. If your cancer comes back, it is worth asking your team whether repeat HER2 testing is appropriate before decisions are made.
Did you know?
HER2 testing is not optional before starting trastuzumab — it is a clinical requirement. Guidelines from NCCN, ASCO and ESMO specify that HER2 status must be confirmed from tumour tissue before the treatment is recommended, because it is not expected to help tumours that do not overexpress the protein.
Getting the right test, and understanding your result, is the starting point for every eligibility conversation.
Source: NCCN Guidelines: Breast Cancer; ASCO/CAP HER2 Testing Guidelines in Breast Cancer
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Common questions
Frequently asked questions
How do I find out if I am HER2-positive?
Your HER2 status is determined by testing your tumour biopsy in a laboratory. If you have already had a biopsy, the test is usually done on that stored tissue — you do not need another procedure. The laboratory scores HER2 protein expression, and if the result is borderline, a second gene-level test is done to confirm it. Ask your oncologist whether HER2 testing has already been ordered and when the result is expected.
Is trastuzumab used for cancers other than breast cancer?
Yes. Trastuzumab is recommended in NCCN and ASCO guidelines for HER2-positive breast cancer, HER2-positive stomach cancer, and HER2-positive cancer of the gastro-oesophageal junction. In each case, HER2-positive status must be confirmed by biopsy testing first. It is not currently standard for other cancer types, though evidence continues to develop. Your oncologist will tell you whether your specific cancer is one where trastuzumab has an established role.
What is the difference between HER2-positive and HER2-low?
HER2-positive means the tumour has a high level of HER2 protein — confirmed by an IHC score of 3+, or 2+ with a positive gene amplification test. Trastuzumab is designed for this group. HER2-low means there is some HER2 protein but not at that level. Trastuzumab is not indicated for HER2-low tumours, but other HER2-directed medicines may be relevant — your oncologist can tell you whether that applies to your situation.
How long does HER2 testing take?
The IHC test usually takes about one to two weeks from when the sample reaches the laboratory. If a second confirmatory test — FISH or SISH — is needed, that adds a few more days. If the original biopsy sample is not suitable, a repeat biopsy would need to be arranged first. Ask your team when the sample was sent and when a result is expected, so you have a timeline rather than an open-ended wait.
What if trastuzumab has to be stopped during treatment?
Treatment may be paused or stopped if heart function changes significantly, if a serious reaction occurs, or if the cancer is not responding. A pause is not necessarily permanent — your team will reassess and explain the options. If treatment has to stop, your oncologist will discuss what the evidence supports for your situation from that point. The right question is what comes next, and that is a conversation your team should be able to have openly with you.
What should I ask my oncologist before starting trastuzumab?
Ask four things: what your HER2 test showed and whether confirmatory testing was done; why trastuzumab is being recommended for your specific cancer type and stage; what the treatment schedule looks like and how it will be given; and what to watch for in terms of side effects, particularly around your heart. Writing the answers down helps, because these conversations are hard to remember afterwards. It is entirely reasonable to ask for your test results in writing.