Trastuzumab (Herceptin®)

Trastuzumab is a targeted therapy drug used to treat HER2 positive breast cancer and some cancers of the stomach or the gullet (oesophagus).

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

Trastuzumab is given into a vein or injected under the skin. You usually have it as an outpatient. Your cancer doctor or nurse will tell you how often you will have it.

Like all targeted therapy drugs, trastuzumab can cause side effects. Some of the side effects can be serious so it is important to read the detailed information below. How targeted therapy affects people varies from person to person. Your healthcare team can talk to you more about this and give you advice on how to manage any side effects.

Tell your doctor or nurse straight away if you:

  • have a temperature
  • feel unwell
  • have severe side effects, including any we don’t mention here.

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

If you need to seek medical attention for any reason other than cancer, always tell the healthcare staff that you are having this treatment.

How trastuzumab works

Trastuzumab is a type of targeted therapy drug called a monoclonal antibody. It works by ‘targeting’ specific proteins on the surface of cells.

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 prevents this by locking on to the HER2 protein. This helps stop the cancer cells from dividing and growing.

How targeted therapies work

This animation shows how targeted therapies work and what effect they have on the body.

About our cancer information videos

How targeted therapies work

This animation shows how targeted therapies work and what effect they have on the body.

About our cancer information videos

When trastuzumab is used

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.

Breast cancer

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 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 chemotherapy or hormonal therapy.

Stomach and oesophageal cancer

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.

We have more about stomach cancer and oesophageal (gullet) cancer.

How trastuzumab is given

You have trastuzumab as a drip into a vein (intravenous infusion) or as an injection under the skin (subcutaneous). You usually have it in the chemotherapy day unit or a clinic.

You usually have trastuzumab every three weeks or once a month. 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.

As a drip

The nurses give you the first dose (infusion) slowly, usually over an hour and a half. You will stay in hospital for a few hours afterwards so they can monitor you for any reaction. If you don’t have any problems with the first treatment, you can have the following infusions over about 30 to 90 minutes and 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. They swap the injection site between your left and right thigh. After the first injection you will be monitored for a few hours to make sure you don’t have a reaction. But after the next injections you’ll be monitored for a shorter time.

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 also having treatment with other cancer drugs, you may have some side effects that we haven’t 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 during treatment

Some people may have side effects while they are being given the treatment or shortly after they have it.

Allergic reaction

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

  • feeling hot or flushed 
  • a skin rash
  • itching
  • shivering
  • feeling dizzy
  • a headache
  • feeling breathless 
  • 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 can happen a few hours after treatment. If you get 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 called neutropenia.

Your doctor may give you antibiotics and other drugs to try to stop you getting an infection. These are called prophylactic medicines.

If you have an infection, it is important to treat it as soon as possible. Contact the hospital straight away on the 24-hour contact number you have 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.

Symptoms of an infection include:

  • feeling shivery
  • a sore throat
  • a cough
  • diarrhoea
  • needing to pass urine often.

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

You will have regular blood tests during treatment. If your white blood cell count is low, your doctor may reduce or delay your treatment for a short time.

Effects on the heart

Trastuzumab may affect the way your 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 stopping 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
  • feel short of breath
  • feel unusually tired or weak (fatigue)
  • have swollen feet, ankles, stomach or lower back
  • have palpitations, which might feel like a thumping or fluttering in your chest
  • have blackouts, or feel light headed or dizzy.

We have more information about heart health and cancer treatment.

Feeling sick

Your doctor can give you anti-sickness drugs to help prevent or control sickness. If you still feel sick, tell your doctor. They can prescribe other anti-sickness drugs that may work better for you.

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 bad 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

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

If your mouth 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.

Abdominal (tummy) pain or indigestion

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

Diarrhoea or constipation

This can usually be easily controlled with medicine, but tell your doctor if it is severe or continues. It's important to drink plenty of fluids if you have diarrhoea.

Drinking at least two litres (three and a half 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.

Feeling tired

Feeling tired is a common side effect. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can give you more energy. If you feel sleepy, do not drive or operate machinery.


This treatment may cause headaches. If this happens, tell your doctor or nurse. They can give you painkillers.

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

Tell your doctor or nurse if you have any of these side effects.

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. If your nails become brittle and break easily, wear gloves when washing dishes or using detergents to help protect them.

Feeling anxious, dizzy or having difficulty sleeping

If you notice any of these effects, talk to your nurse or doctor.

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.

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.

Other information about trastuzumab

Other medicines

Some medicines can affect trastuzumab or be harmful when you are having it. This includes medicines you can buy in a shop or chemist. Tell your cancer doctor about any medicines you are taking, including vitamins, herbal drugs and complementary therapies.


Your doctor will advise you not to get pregnant or father a child while having this treatment and for some time afterwards. The drugs may harm the developing baby. It is important to use effective contraception.


Women are advised not to breastfeed while having this treatment and for some time afterwards. This is because the drugs could be passed to the baby through breast milk.


Doctors don’t yet know how this treatment may affect your fertility (the ability to become pregnant or father a child). If you are worried about this, talk to you doctor before treatment starts.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses that 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 this treatment.