Medical Oncologist
HER2-positive cancer
Trastuzumab Myths: — What the Evidence Actually Shows
If you have just been prescribed trastuzumab, you may have been told it is chemotherapy, or assumed it works the same way. It does not. Understanding the difference tells you which side effects to prepare for — and which worries you can set aside.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Not chemotherapy — Trastuzumab is a monoclonal antibody. It works through a different mechanism and causes different side effects.
- HER2-positive only — It is prescribed only when your tumour tests positive for HER2 overexpression. It does not work on HER2-negative cancers.
- Hair loss is not expected — Hair loss comes from chemotherapy, not from trastuzumab. If you are having both, the chemotherapy is the cause.
- Heart monitoring matters — Trastuzumab can affect heart function in a proportion of patients. Regular checks are part of the treatment plan, not a sign something has gone wrong.
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Trastuzumab is not chemotherapy. It is a monoclonal antibody that binds to the HER2 protein on cancer cell surfaces and blocks growth signals. Chemotherapy attacks all rapidly dividing cells. Trastuzumab targets only HER2-positive cells, works differently, and causes different side effects.
What do people get wrong about trastuzumab?
Trastuzumab is a type of chemotherapy.
Trastuzumab is a monoclonal antibody, not a chemotherapy drug. Chemotherapy damages all rapidly dividing cells throughout the body. Trastuzumab is a laboratory-made protein that binds specifically to the HER2 receptor on cancer cell surfaces and blocks the signal that drives tumour growth. The confusion is understandable — both are given as intravenous infusions, often in the same oncology unit — but the mechanism, the targets, and the side effect profile are different.
It will cause my hair to fall out.
Hair loss is a side effect of chemotherapy, not of trastuzumab. Chemotherapy damages hair follicles because they divide rapidly, and trastuzumab does not have that effect. Many people with HER2-positive cancer receive trastuzumab alongside chemotherapy, and hair loss during that period comes from the chemotherapy component. If you are receiving trastuzumab on its own, hair loss is not an expected side effect.
It works for all breast cancer patients.
Trastuzumab only benefits patients whose tumour overproduces the HER2 protein. If your pathology report does not show HER2-positive status, the drug has no target to bind to and will not be prescribed. HER2 testing is done routinely on every breast cancer biopsy. The belief that trastuzumab is broadly useful comes partly from news coverage that does not always explain the HER2-positive requirement.
Because it is targeted, it has no side effects.
Trastuzumab is more precise than chemotherapy, but it can still affect healthy tissue. HER2 receptors exist in heart muscle cells as well as cancer cells, and trastuzumab can reduce the heart's pumping efficiency in a proportion of patients. ASCO and NCCN guidelines recommend regular heart function monitoring throughout treatment. Most changes are caught before you feel anything and are reversible when treatment is adjusted promptly — which is why the monitoring schedule matters.
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Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
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MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
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MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
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Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
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MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
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What is trastuzumab, and how does it work?
Trastuzumab is a monoclonal antibody — a protein designed in a laboratory to recognise a specific target. In HER2-positive cancers, the HER2 gene is overactive, causing tumour cells to display large amounts of the HER2 protein on their surface. Trastuzumab binds to that protein.
Once bound, it blocks the signal telling the cancer cell to grow. It also flags the cell for destruction by your immune system. These two actions only work when HER2 is overexpressed — which is why testing comes before prescribing, and why the result on your pathology report matters.
At CION, trastuzumab is given as a day-care infusion. You do not need to be admitted overnight. The first dose takes longer to administer; subsequent doses are shorter once your team is satisfied with how you have responded.
What side effects should you actually expect?
The most significant real risk is cardiac. Because HER2 receptors are present in heart muscle as well as cancer cells, trastuzumab can reduce how effectively the heart pumps in a proportion of patients. ASCO guidance recommends a heart function scan — usually an echocardiogram — before treatment starts and at regular intervals during it.
Most cardiac changes are detected before you feel anything and are reversible when treatment is paused or adjusted. This is why attending every monitoring appointment matters, not just the infusion sessions.
Infusion reactions — chills, mild fever, or flushing during the first treatment — can occur and are managed in the day-care unit while the infusion is running. Tiredness and joint or muscle aches are reported by some patients. Both are generally milder than the fatigue associated with chemotherapy and worth mentioning to your team so they can be managed.
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Common questions
Frequently asked questions
Will I lose my hair on trastuzumab?
Hair loss is not an expected side effect of trastuzumab on its own. If you are also receiving chemotherapy — which is common in HER2-positive breast cancer — hair loss comes from the chemotherapy component, not from trastuzumab. If you are uncertain which parts of your treatment plan are which, ask your oncologist to explain each drug's role separately, so you know what to expect from each one.
Why do I need heart tests every few months?
Trastuzumab can reduce the heart's pumping efficiency in a proportion of patients, because HER2 receptors exist in heart muscle as well as cancer cells. ASCO and NCCN guidelines recommend regular heart function monitoring — typically an echocardiogram — before treatment starts and at intervals during it. The monitoring is not a sign something has already gone wrong. It is how your team catches any change early, while it is still reversible.
How long will I need to take trastuzumab?
The duration depends on your specific situation — the cancer stage, whether other treatments are being given alongside it, and how your body responds. For early HER2-positive breast cancer, NCCN and ESMO guidelines recommend approximately one year of treatment in most cases. For advanced or metastatic disease, the approach differs, and your oncologist will explain what applies to you. Do not adjust the schedule yourself — the timing is part of how the treatment is planned.
Is the biosimilar version as effective as Herceptin?
Biosimilars approved by CDSCO in India are assessed for equivalence to the reference product Herceptin before they are permitted. They are required to demonstrate that they work in the same way and are acceptably safe. The biosimilar your team prescribes will have gone through that regulatory process. If you have concerns about the specific product being offered, ask your oncologist to explain the basis for the choice — that is a reasonable question to raise.
Can I have trastuzumab if I already have a heart condition?
That depends on the nature of your condition and how well it is controlled. Because trastuzumab can affect heart function, existing cardiac problems require careful assessment before treatment starts. Your oncologist will review your cardiac history and may request a cardiology opinion before proceeding. In some cases treatment goes ahead with closer monitoring; in others a different approach is taken. Do not assume a heart condition rules you out — that is a conversation your team needs to have with the clinical detail in front of them.