Trastuzumab

Antineoplastic monoclonal antibodies
Antineoplastic monoclonal antibodies
High alert
An error with this medicine can cause serious harm: double checks and protocols are used.
Pregnancy: avoid
Avoid in pregnancy. Can harm the fetus (including too little amniotic fluid); pregnancy is avoided during treatment and for several months after the last dose.

An anti-HER2 antibody for HER2-positive breast and stomach cancer. Its key risk is heart failure, so the heart's pumping is checked before and during treatment.

Updated Nov 1, 2026

Also called: anti-HER2 antibody

Quick facts

Group: Antineoplastic monoclonal antibodies
Target: HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IV
Used for: HER2-overexpressing breast cancer
Key effects: Infusion reactions · Diarrhoea · Muscle
Monitor: Ejection fraction · Baseline ECG
ATC: L01FD01

No doses: the clinician sets them by the current guideline.

Mechanism of action

HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IVTrastuzumab

The cryo-EM structure shows the HER2 extracellular domain with two antibody arms bound at once: trastuzumab on domain IV and pertuzumab on domain II.

Target in 3D: HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IV. PDB structure 6OGE (RCSB PDB, public domain). View the structure at RCSB PDB

About one in four or five breast cancers carries many copies of the ERBB2 gene and overexpresses HER2, which signals for growth even without a ligand. Trastuzumab, a humanised IgG1, binds domain IV of the HER2 extracellular region, reduces HER2 signalling and marks the cell for antibody-dependent cellular cytotoxicity. It only helps tumours with HER2 overexpression or amplification. HER2 signalling also keeps heart muscle working, which explains its cardiotoxicity.

HER2-amplified tumour cells overexpress HER2
Trastuzumab binds HER2 domain IV
Growth signalling falls; immune cells kill (ADCC)
Loss of HER2 signal in heart muscle: cardiotoxicity

Indications

HER2-overexpressing breast cancer, early (adjuvant) or metastatic, usually with a taxane or other chemotherapy. Breast cancer →
HER2-overexpressing metastatic gastric or gastro-oesophageal junction cancer, with chemotherapy. Gastric cancer →

Adverse effects

Common

Infusion reactions: fever, chills, nausea, headache, rash
Diarrhoea, abdominal pain
Muscle, joint and back pain
Insomnia
Tingling of hands and feet

Contraindications

Symptomatic heart failure or a low ejection fraction before starting
HER2-negative tumours (no benefit)

Key interactions

Anthracyclines (doxorubicin, epirubicin): Together they cause much more left ventricular dysfunction; they are usually given one after the other, not at the same time.
Taxanes (paclitaxel, docetaxel): The usual partners; the cardiac risk is much lower than with anthracyclines.

What is monitored

Ejection fraction (echocardiogram or radionuclide scan) before starting and regularly during and after treatment
Baseline ECG
Symptoms of heart failure: breathlessness, oedema, rapid weight gain
Pregnancy test before starting

Administration and safety

Intravenous infusion only, never as a push or bolus; watch for chills and fever during and after the infusion.
Look-alike names: trastuzumab, ado-trastuzumab emtansine and fam-trastuzumab deruxtecan are different drugs and are never substituted for one another.
The intravenous and subcutaneous (with hyaluronidase) products are not interchangeable.
Confirm that a recent ejection fraction result is on file before each cycle.

Pregnancy and breastfeeding

Avoid in pregnancy. Can harm the fetus (including too little amniotic fluid); pregnancy is avoided during treatment and for several months after the last dose.

Nursing care

Check vital signs and look for infusion reactions during and after the infusion.
Ask at each visit about breathlessness, cough, ankle swelling and palpitations; weigh the patient.
Make sure cardiac imaging is scheduled as ordered.
Teaching: report sudden weight gain, swelling or shortness of breath; use effective contraception during treatment and for months after.

Pharmacokinetics

Absorption: Intravenous infusion (a subcutaneous form with hyaluronidase also exists).
Elimination: Removed like other IgG antibodies; levels take months to reach steady state.
Half-life: Several days to weeks, depending on the schedule.

Test yourself

Think of the answer, then tap the question to see it.

Which test on the tumour decides whether trastuzumab is used?

HER2 testing: protein overexpression (immunohistochemistry) or gene amplification (in situ hybridisation).

Why does trastuzumab cause heart failure?

HER2 signalling is needed to keep cardiomyocytes contracting normally; blocking it reduces ejection fraction.

Which combination raises trastuzumab's cardiac risk the most?

Combination with an anthracycline such as doxorubicin.

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Connections

← Back to the class: Antineoplastic monoclonal antibodies

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Trastuzumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).

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Representative model, for educational purposes only.