Trastuzumab (Herceptin and biosimilars)

Medicine at a glance

Trastuzumab is a targeted antibody treatment that attaches to a protein called HER2. Tests on a cancer sample help the team decide whether this treatment is appropriate. It is commonly given through a vein, usually weekly or every three weeks. Certain formulations are injected under the skin every three weeks. Your prescription identifies the exact product and route.

The most important precautions concern heart function, reactions during or after administration, lung problems and pregnancy. You need heart checks even if you feel well. Side effects also depend on other medicines in your treatment plan; chemotherapy can add infection risk, nausea, hair loss and other effects.

Keep your treatment record and urgent contact number accessible, and follow your team’s individual instructions.

What trastuzumab is and how it works

HER2 helps cells receive growth signals. Some cancers have too much HER2 protein or extra copies of the gene that makes it. Trastuzumab binds to HER2, interferes with growth signalling and helps immune cells recognise and attack cancer cells. It is a monoclonal antibody, a laboratory-made protein designed to recognise a particular target.

This is targeted antibody therapy. Although immune cells contribute to its action, it is different from an immune-checkpoint inhibitor. It is also different from an antibody–drug conjugate, which carries an attached cancer-killing drug. Herceptin must not be confused with trastuzumab deruxtecan, called Enhertu, or trastuzumab emtansine, called Kadcyla. Their doses, schedules and major risks differ.

Names and formulations

Herceptin is the original brand. Verified intravenous biosimilar brands include Hercessi, Herzuma, Kanjinti, Ogivri, Ontruzant and Trazimera. Biosimilars are assessed against the reference medicine to confirm that there are no clinically meaningful differences in safety and effectiveness. A different brand name does not mean a weaker treatment. The pharmacist should record the actual product you receive.

Herceptin Hylecta is a US under-the-skin formulation containing trastuzumab and hyaluronidase, an enzyme that helps the injection spread locally. European Herceptin also has a specific subcutaneous formulation. Phesgo contains both pertuzumab and trastuzumab with hyaluronidase. It is a separate combination product with its own instructions. A switch between products must be organised by your treatment team.

How the team decides whether it is suitable

Your team reviews the cancer's HER2 result, your diagnosis, previous treatments and the intended treatment goal. HER2 testing may measure protein staining, called immunohistochemistry or IHC, or gene amplification, using a test such as ISH. The method and interpretation depend on the tumour type. An unclear result may require further testing.

The words “HER2-low” or “HER2-ultralow” in information about another medicine do not automatically establish suitability for ordinary trastuzumab. Ask the oncologist to explain your own pathology result and why this particular treatment has been chosen. Do not substitute one HER2-directed medicine for another on the basis of similar names.

Heart health is central to the decision. Tell the team about heart failure, angina, a previous heart attack, irregular heartbeat, high blood pressure or previous chest radiotherapy. Previous anthracycline chemotherapy, such as doxorubicin or epirubicin, also matters. European Herceptin information rules out treatment for severe breathlessness at rest due to advanced cancer or a need for supplementary oxygen. Other lung disease and previous antibody reactions also need assessment.

Before treatment starts

You will usually have a clinical assessment, blood tests and a heart scan. An echocardiogram uses ultrasound to assess the heart; a MUGA scan is another way of measuring its pumping function. The result includes the left ventricular ejection fraction, or LVEF, which estimates how much blood the main pumping chamber pushes out with each beat. An ECG may assess rhythm.

Bring a complete list of prescribed medicines, non-prescription remedies, vitamins and herbal products. Explain any previous allergy, including reactions to a cancer infusion or injection. Pregnancy testing is needed where relevant, and contraception, fertility and breastfeeding should be discussed before the first treatment.

Ask which product you will receive, how long the visit takes and whether someone should accompany you. If you feel unwell before an appointment, call the unit rather than arriving without warning or deciding yourself to miss treatment.

Blood counts, kidney function and liver tests help assess your whole regimen. Additional checks may be needed because of chemotherapy or another targeted medicine. The pharmacy prepares and stores these products under controlled conditions; they are not medicines to mix or inject yourself.

How trastuzumab is given

Intravenous treatment

Intravenous trastuzumab is infused through a cannula, central line or implanted port. It must not be given as a rapid intravenous push. A first dose is usually infused over 90 minutes. Later infusions may take 30 minutes if the first was well tolerated, although the prescribed regimen may specify 30–90 minutes.

The dose is calculated from body weight. Common schedules use a loading dose of 4 mg/kg followed by 2 mg/kg weekly, or a loading dose of 8 mg/kg followed by 6 mg/kg every three weeks. These are examples, not instructions for calculating your own dose. The first larger dose helps establish the required drug exposure; it does not mean your cancer has suddenly worsened.

European intravenous Herceptin instructions specify observation for at least six hours from the start of the first infusion and two hours from the start of later infusions. These intervals are measured from the start, not added in full after the drip finishes. US instructions require monitoring and management of reactions without prescribing this identical routine timetable. Follow your unit's product-specific plan.

Under-the-skin treatment

The separate subcutaneous trastuzumab formulation provides a fixed 600 mg dose every three weeks, without a loading dose or adjustment for body weight. Herceptin Hylecta contains 600 mg trastuzumab and 10,000 units hyaluronidase in 5 mL. It is injected by a healthcare professional into the thigh over approximately two to five minutes. The team alternates thighs and avoids damaged or inflamed skin.

European subcutaneous Herceptin instructions specify observation for 30 minutes after the first injection and 15 minutes after subsequent injections. The US Hylecta label emphasises close monitoring, particularly for the first administration, without assigning the same fixed observation times. An injection is shorter than an infusion but still requires supervision and access to emergency treatment.

Phesgo is different: its initial and maintenance injections contain two cancer antibodies and have different volumes, injection times and delayed-dose rules. If your prescription changes to Phesgo, obtain that product's plan rather than continuing to use the single-agent trastuzumab instructions.

Delayed appointments and treatment duration

Contact the unit promptly if you miss an appointment. For intravenous Herceptin, a delay of one week or less beyond the due date generally calls for the usual maintenance dose as soon as possible. A delay of more than one week calls for a new loading dose under the reviewed labels. This is time overdue, not simply time since the last infusion. Combination regimens may have their own instructions.

For subcutaneous Herceptin or Hylecta, a missed dose is given as soon as possible and later injections should be at least three weeks apart. Do not apply the intravenous loading-dose rule to these injections. Phesgo has a separate six-week interval rule. The prescribing team will issue the revised calendar.

Some treatment plans last about a year; others continue while benefit persists and side effects remain acceptable. Ask about your planned endpoint. If you vomit after an infusion or injection, the medicine has already entered your body: you do not need a replacement dose. Report persistent vomiting so its cause and dehydration risk can be assessed.

Monitoring and checking whether treatment is working

Heart scans are repeated because a decline in pumping function may have no early symptoms. US Herceptin and Hylecta guidance recommends LVEF assessment before treatment, every three months during treatment and at completion. If treatment is withheld for significant heart dysfunction, repeat checks are recommended at four-week intervals.

For treatment given to reduce recurrence risk, US guidance recommends LVEF checks every six months for at least two years after completion. European guidance includes checks every three months during treatment and every six months after stopping until 24 months from the last dose. In the early-treatment setting following anthracyclines, European guidance recommends further annual monitoring up to five years, or longer if LVEF continues to fall. Your cardiology and oncology teams individualise this schedule.

Blood tests and clinical review assess the wider treatment plan. Scans, examination and symptoms help evaluate cancer control where appropriate. Side-effect severity does not reliably tell you whether trastuzumab is working; feeling well does not mean it is ineffective.

Keep track of breathlessness, swelling, exercise tolerance and any changes your team asks you to monitor. Tell the team about symptoms between appointments rather than waiting for the next scheduled scan. A treatment pause may protect your heart and does not by itself mean the cancer treatment has failed.

Common side effects and practical management

Tiredness, aches and headache

Fatigue, headache, muscle aches and joint discomfort can occur. Plan manageable activity and rest, and accept practical help when needed. Persistent or disabling fatigue warrants assessment because anaemia, infection or a heart problem may contribute. Check which pain medicine is suitable before taking it regularly.

Arrange help with driving after your first treatment if advised. Do not drive when dizzy, sleepy or unwell, or while experiencing a treatment reaction. Symptoms that are new, severe or different from your usual pattern should be reported.

Nausea, appetite and bowel changes

Small meals and prescribed anti-sickness medicine can help nausea. Tell the team if you cannot eat or drink adequately. Diarrhoea may occur, especially with certain partner treatments. Record how many stools you pass compared with normal, use prescribed treatment as directed and take fluids according to your individual plan.

Seek urgent advice for persistent diarrhoea, dizziness, very little urine, blood in stool, fever or inability to keep fluids down. Do not force large amounts of fluid if you have a heart or kidney condition; ask for a suitable target. Significant weight loss or continuing appetite problems can be helped by a dietitian.

Skin, mouth and injection-site symptoms

Rash, dry skin or itching may occur. Use gentle skin care and ask about suitable moisturisers. Mouth soreness is more likely with some combined regimens; report ulcers or difficulty eating and follow the team's mouth-care advice. Blistering, a rapidly spreading rash or rash with breathing difficulty needs urgent assessment.

A subcutaneous injection can cause local pain, redness or swelling. Tell the nurse if discomfort is substantial or the area is worsening, hot or spreading. Local injection discomfort is different from a whole-body allergic reaction, which may include wheezing, faintness or facial swelling.

Effects of the whole regimen

Hair loss, numbness in fingers or toes and low blood counts may be strongly influenced by accompanying chemotherapy. Ask which medicine is likely responsible and what can help. Do not assume every symptom comes from trastuzumab or that finishing chemotherapy removes all need for heart monitoring.

Important risks that need medical assessment

Heart weakness and rhythm problems

Trastuzumab can weaken the heart muscle, sometimes causing heart failure. It can also be associated with rhythm problems and high blood pressure. Report new breathlessness on exertion, difficulty breathing when lying flat, swollen ankles, palpitations, rapid weight gain or unusual exhaustion. Severe breathlessness, chest pain or collapse requires emergency care.

The risk is greater with anthracycline exposure, particularly when treatments overlap. A normal baseline scan does not remove the risk. Some patients improve with a pause and heart medicines, but recovery is not guaranteed. Continuing or restarting requires a specialist assessment of cancer benefit and cardiac risk.

US and European thresholds and reassessment intervals for holding treatment are not identical. Your team considers both the LVEF value and the change from your own baseline. Treatment is usually withheld or stopped for important toxicity rather than simply reduced according to how tired you feel. US instructions require permanent withdrawal if the LVEF decline lasts over eight weeks or treatment has been held for heart dysfunction more than three times.

Infusion reactions and severe allergy

Reactions may cause chills, fever, flushing, rash, headache, nausea, dizziness, wheeze or a change in blood pressure. Tell the nurse immediately, even if symptoms seem mild. The infusion may be slowed or stopped and medicines given. A mild reaction does not necessarily rule out further treatment. US instructions require stopping intravenous Herceptin for severe or life-threatening reactions, and permanently stopping Hylecta for anaphylaxis or severe hypersensitivity.

Serious allergy can cause throat or facial swelling, breathing difficulty or fainting. It needs immediate emergency treatment. Although reactions often begin during administration or within 24 hours, delayed reactions and worsening after initial improvement have been reported. Do not assume you are safe to ignore symptoms because the observation period is over.

Lung problems

Trastuzumab can cause serious lung inflammation and other pulmonary complications, sometimes independently of an immediate infusion reaction. A new cough, fever or increasing breathlessness needs prompt assessment. Infection, heart failure and treatment-related inflammation can feel similar, so do not try to distinguish them at home. Severe breathing difficulty is an emergency.

Previous lung disease, breathing difficulty at rest and certain accompanying treatments can increase concern. Tell the team if you need oxygen or if your usual oxygen requirement changes. The team may pause treatment and arrange scans, blood tests or other investigations. US instructions require discontinuation for interstitial pneumonitis, a type of lung inflammation, or acute respiratory distress syndrome, a severe breathing failure.

Infection, bleeding and other reported problems

Trastuzumab can increase chemotherapy-associated low neutrophil counts and fever with neutropenia. Neutrophils are white blood cells that fight infection. Follow your team's temperature threshold and call urgently for fever, shaking chills or feeling severely unwell, even without fever. Do not wait for the next blood test.

Report unusual bruising, pinpoint skin spots, bleeding or blood in urine. Immune-related low platelets and kidney filtering problems have been reported after treatment entered wider use. New marked swelling, frothy urine or reduced urine also needs assessment. These reports do not establish how frequently such events occur.

Possible tumour lysis syndrome has been reported, especially with a large amount of cancer. Rapid cell breakdown can disturb blood salts and kidney function. The team may arrange extra tests when relevant. Marked weakness, persistent vomiting, reduced urine, muscle cramps, palpitations or confusion needs urgent assessment rather than waiting for routine review.

Other medicines, supplements and vaccines

Tell every clinician about recent trastuzumab, even after treatment has finished. It can persist in the circulation for months. Both US and European guidance advise avoiding anthracycline chemotherapy for up to seven months after stopping, if possible, because of heart risk. If an anthracycline is necessary, close cardiac monitoring is required. This is a specialist sequencing decision, not a reason to independently refuse or delay prescribed treatment.

Have new medicines, herbal remedies and supplements checked. There is no routine food-timing or stomach-acid-medicine spacing rule for the injected antibody itself, but partner medicines may have restrictions. Tell the team before taking medicines for breathlessness, swelling or chest symptoms; these symptoms first need assessment.

Vaccination advice depends on the complete regimen and immune status. Discuss non-live vaccines and timing with the team. Live vaccines may be unsuitable during immune-suppressing treatment and for a period afterwards; there is no single interval that fits every trastuzumab combination.

Everyday life during treatment

Many people can continue some usual activities, although the amount varies with chemotherapy, fatigue and clinic visits. Use gentle activity within your ability, and report a new reduction in exercise tolerance rather than assuming it is only loss of fitness. Avoid driving if dizzy, sleepy or affected by a reaction.

Plan travel around treatment and monitoring, with access to medical advice. Carry the exact product name and recent treatment dates. Ask before changing an appointment, as an intravenous delay can affect the dose required when treatment resumes.

Eat food you can tolerate and ask for help with weight loss. Discuss alcohol in relation to your liver, heart and other medicines. Tell dentists and surgeons about your cancer treatment; procedure timing depends on the whole regimen and current health.

Ask what scan or heart-test results mean for your next treatment. Support with anxiety, sleep, work and intimacy is also part of care.

Fertility, contraception, pregnancy and breastfeeding

Trastuzumab can harm a developing baby. Reported effects include too little amniotic fluid, which can affect kidney and lung development and can be life-threatening. Pregnancy testing is required before treatment where relevant. Use effective contraception during treatment and for seven months after the last dose.

Contact the team promptly if pregnancy is possible during treatment or within that seven-month period. Specialist pregnancy assessment and monitoring are needed; do not wait for the next routine appointment. Your team can help choose contraception appropriate to your cancer and other treatments.

The effect of trastuzumab alone on human fertility is not established. Chemotherapy or hormonal treatment given alongside it can affect fertility. Discuss preservation options before treatment when relevant. The reviewed trastuzumab labels do not prescribe a universal male contraception interval; accompanying medicines may require one, so male patients should ask about their complete regimen.

Breastfeeding advice differs between authorities. European Herceptin information says not to breastfeed during treatment or for seven months afterwards. US Herceptin and Hylecta information calls for an individual benefit–risk discussion, taking the seven-month washout period into account, rather than stating the same blanket prohibition. Do not start or restart breastfeeding without a specific plan that also considers partner medicines.

After a pause or when treatment finishes

Continue planned heart follow-up and report new breathlessness or swelling after the last dose. A completed cancer-treatment course does not mean heart monitoring stops that day. Keep an accurate last-dose date for future medicine decisions and the seven-month pregnancy precaution.

If treatment was paused because of heart dysfunction or a reaction, the team decides whether and how it can restart. Do not interpret a better symptom day as clearance. Ask for the updated product, dose and calendar, and clarify whether any premedication or additional observation is planned.

Keep attending cancer follow-up and use the urgent advice service for concerning symptoms between visits. There is no home supply to taper yourself. The next step may be monitoring, another treatment or ongoing supportive care according to your individual plan.

Frequently asked questions