What is trastuzumab?

Trastuzumab is used to treat:

  • HER2 positive breast cancer
  • HER2 positive cancers of the stomach or gullet (oesophagus).

It is best to read this information with our general information about the type of cancer you have.

Trastuzumab is a type of targeted therapy drug called a monoclonal antibody. It is often given in combination with other cancer drugs such as chemotherapy.

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment.

Trastuzumab is not the same as trastuzumab emtansine (Kadcyla®). We have separate information about trastuzumab emtansine (Kadcyla®).

What is HER2?

Some cancers have too much of a protein called HER2 (human epidermal growth factor receptor 2) on the surface of their cells. These are called HER2 positive cancers. The extra HER2 proteins stimulate the cancer cells to divide and grow.

Trastuzumab stops this by locking on to the HER2 protein. This helps stop the cancer cells from dividing and growing. Trastuzumab is used to treat HER2 positive cancer. The only way to check if a cancer is HER2 positive is to test the cancer cells. Tests can be done on samples of cells taken during a biopsy of the cancer or surgery to remove the cancer.

When is trastuzumab used?

Trastuzumab is often used to treat HER2 positive breast cancer. It may be given with or after chemotherapy to reduce the risk of the cancer coming back. It is also sometimes given along with another targeted therapy drug called pertuzumab (Perjeta®).

Trastuzumab is also used to treat HER2 positive breast cancer that has come back or spread to other parts of the body (secondary breast cancer). It may be given on its own or with other drugs such as pertuzumab and chemotherapy.

Trastuzumab is sometimes used with chemotherapy to treat advanced HER2 positive cancer that started in the:

  • stomach
  • part of the gullet (oesophagus) nearest to the stomach.

How is trastuzumab given?

You will be given trastuzumab at a day unit. It can be given on its own or in combination with other cancer drugs.

During treatment you usually see a cancer doctor, a cancer nurse or specialist nurse, and a specialist pharmacist. This is who we mean when we mention doctor, nurse or pharmacist in this information.

Before or on the day of treatment, a nurse or person trained to take blood (phlebotomist) will take a blood sample from you. This is to check that your blood cells are at a safe level to have treatment.

You will see a doctor or nurse before you have treatment. They will ask you how you have been feeling. If your blood results are okay, the pharmacist will prepare your targeted therapy. Your nurse will tell you when your treatment is likely to be ready.

The drug can be given as a drip into a vein (intravenous infusion) or as an injection under the skin (subcutaneous).


As a drip

The nurses give you the first dose (infusion) slowly, usually over an hour and a half. After the infusion, you will stay in hospital for a few hours so they can monitor you for any reaction. If you do not have any problems with the first treatment, you can have the following infusions over about 30 to 90 minutes. You will be able to go home an hour later.


As an injection under the skin

A nurse gives you the injection into your thigh. This only takes a few minutes. The nurse will swap the injection site between your left and right thigh. After the first injection, the nurse will monitor you for a few hours to make sure you do not have a reaction. After the next injections you will be monitored for a shorter time.


Your course of treatment

You usually have trastuzumab every 3 weeks or once a week. If you have early stage breast cancer, you will have trastuzumab for a year. If the cancer is advanced or has spread, you may have trastuzumab for as long as it is controlling the cancer. Your nurse, pharmacist or doctor will discuss your treatment plan with you.

About side effects

We explain the most common side effects of this treatment here. We also include some less common side effects. You may get some of the side effects we mention, but you are unlikely to get all of them.

If you are having trastuzumab with chemotherapy, you are more likely to get these side effects. If you are also having treatment with other cancer drugs, you may also have some side effects that we have not listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.

Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.

Serious and life-threatening side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Side effects while treatment is being given

Some people have an allergic reaction while having this treatment. Signs of a reaction can include:

  • feeling hot or flushed
  • shivering
  • itching
  • a skin rash
  • feeling dizzy
  • a headache
  • feeling breathless or wheezy
  • swelling of your face or mouth
  • pain in your back, tummy or chest.

Your nurse will check you for signs of a reaction during your treatment. If you feel unwell or have any of these signs, tell them straight away. If you do have a reaction, it can be treated quickly.

Sometimes a reaction happens a few hours after treatment. If you develop any signs or feel unwell after you get home, contact the hospital straight away.

Common side effects of trastuzumab

Risk of infection

This treatment can reduce the number of white blood cells in your blood. These cells fight infection. If the number of white blood cells is low, you are more likely to get an infection. A low white blood cell count is sometimes called neutropenia.

An infection can be very serious when the number of white blood cells is low. It is important to get any infection treated as soon as possible. Contact the hospital straight away on the 24-hour contact number you have been given if:

  • your temperature goes over 37.5°C (99.5°F)
  • you suddenly feel unwell, even with a normal temperature
  • you have symptoms of an infection
  • your temperature goes below 36°C (96.8°F).

Symptoms of an infection include:

  • feeling shivery and shaking
  • a sore throat
  • a cough
  • breathlessness
  • diarrhoea
  • needing to pass urine (pee) a lot or discomfort when you pass urine.

It is important to follow any specific advice your cancer treatment team gives you.

The number of white blood cells will usually return to normal before your next treatment. You will have a blood test before having more treatment. If your white blood cell count is low, your doctor may delay your treatment for a short time, until your cell count increases.

Effects on the heart

Trastuzumab can affect the way the heart works. Before you start treatment, your doctor will check your heart health and arrange some tests. You will have these tests again during and after treatment. If the tests show signs of heart changes or you develop symptoms of heart problems, these can be treated with tablets.

Sometimes the symptoms of heart problems are like the symptoms of other conditions. But it is best to get any new symptom checked by your doctor. Always tell your doctor if you:

  • have chest discomfort, pain or tightness
  • have pain that spreads to your arm, neck, jaw, stomach or back
  • have palpitations, which might feel like a thumping or fluttering in your chest
  • feel short of breath
  • feel unusually tired or weak (fatigue)
  • have swelling of the feet, ankles, stomach or lower back
  • faint (have blackouts), or feel light headed or dizzy.

Feeling sick

This is usually mild. Your doctor can prescribe anti-sickness drugs to help. Tell your doctor if it does not get better.

Loss of appetite

This treatment can affect your appetite. Do not worry if you do not eat much for a day or two. But if your appetite does not come back after a few days, tell your nurse or dietitian. They will give you advice. They may give you food or drink supplements.

Changes to your taste

You may get a bitter or metal taste in your mouth. Sucking sugar-free sweets may help with this. Some foods may taste different or have no taste. Try different foods to find out what tastes best to you. Taste changes usually get better after treatment finishes. Your nurse can give you more advice.

Sore mouth and throat

This treatment may cause a sore mouth and throat. You may also get mouth ulcers. This can make you more likely to get a mouth or throat infection. Use a soft toothbrush to clean your teeth or dentures in the morning, at night and after meals.

If your mouth or throat is sore:

  • tell your nurse or doctor – they can give you a mouthwash or medicines to help
  • try to drink plenty of fluids
  • avoid alcohol, tobacco, and foods that irritate your mouth and throat.

Sucking ice chips may sometimes help relieve mouth or throat pain. But if you are having radiotherapy to the head or neck, do not suck on ice. It can cause damage.

Abdominal (tummy) pain or indigestion

Tell your doctor or nurse if you have tummy pain or indigestion. They can prescribe drugs to help.

Diarrhoea or constipation

This can usually be easily controlled with medicine, but tell your doctor if it is severe or continues. It is important to drink plenty of fluids if you have diarrhoea. Drinking at least 2 litres (3 ½ pints) of fluids every day will help with constipation. Try to eat more foods that contain fibre (such as fruit, vegetables and wholemeal bread) and do some regular, gentle exercise.


This treatment may cause headaches. If you have headaches, tell your doctor. They may give you painkillers to help.

Joint and muscle pain

You may have pain and stiffness in your joints, and sometimes in your muscles. Tell your doctor or nurse if this happens. They can prescribe painkillers and give you advice.

Watery, sore eyes

Your eyes may become watery. Sometimes they may become sore and inflamed (conjunctivitis). Your doctor can prescribe eye drops if you need them.

Blocked or runny nose, or nose bleeds

These side effects are not usually serious but tell your doctor or nurse if you have any of them. They may be able to help if you find them difficult to cope with.

Numb or tingling hands or feet (peripheral neuropathy)

This treatment may affect the nerves, which can cause numb, tingling or painful hands or feet. You may find it hard to fasten buttons or do other fiddly tasks. Tell your doctor if you have these symptoms.

Skin or nail changes

Tell your doctor if you get a skin rash. Your nails also might become brittle and break easily. If this happens, wear gloves when washing dishes or using detergents to help protect them.

Difficulty sleeping

This treatment can cause sleeplessness (insomnia) in some people. If you are finding it difficult to sleep, talk to your doctor or specialist nurse.

Effects on the lungs

This treatment can cause changes to the lungs. Tell your doctor if you develop:

  • a cough
  • wheezing
  • a fever (high temperature)
  • breathlessness.

You should also tell them if any existing breathing problems get worse. You may have tests to check your lungs.

Problems at the injection site

If you are having trastuzumab as an injection under the skin, you may have discomfort, mild stinging, bruising or redness in the injection area. This is usually mild and temporary.

Other information about trastuzumab

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:

  • throbbing pain, redness or swelling in a leg or arm
  • suddenly feeling breathless or coughing
  • sharp chest pain, which may be worse when you cough or take a deep breath.

If you have any of these symptoms, contact the hospital straight away on the 24-hour contact number you have been given. If you cannot get through to your doctor, call the NHS urgent advice number on 111.

A blood clot is serious, but it can be treated with drugs that thin the blood (anticoagulants). Your doctor or nurse can give you more information.

You can help reduce the risk of developing a blood clot by:
  • staying active during treatment
  • drinking plenty of fluids, especially water.

You may be given anticoagulants to help prevent a clot.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.


Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.


You are advised not to breastfeed while having this treatment, or for some time after treatment finishes. This is because the drugs could be passed to the baby through breast milk.

Your doctor or nurse can give you more information.


It is not known if trastuzumab may affect your fertility (your ability to get pregnant or father a child). If you are worried about this, you can talk to your doctor or nurse before treatment starts.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.