Trastuzumab is a targeted cancer drug and is also known by other names such as Herceptin, Herzuma and Ontruzant. It is a treatment for early and advanced breast cancer, advanced stomach cancer and cancer of where the food pipe joins your stomach (gastro oesophageal junction).

What is trastuzumab?

Trastuzumab is a targeted cancer drug. It is a treatment for cancers that have large amounts of a protein called human epidermal growth factor receptor 2 (HER2) Open a glossary item, such as:

  • early breast cancer (the cancer hasn't spread beyond the breast or the lymph nodes in the armpit on the same side of the body. So, the cancer hasn't spread to any other part of the body)
  • breast, stomach and gastro oesophageal junction cancer that has spread to another part of the body (advanced or metastatic cancer)

You might have the original drug called Herceptin, or a biosimilar such as Herzuma or Ontruzant. A biosimilar is a very similar copy of the original drug, but it is not exactly the same. Biosimilars undergo strict testing to check they work just as well as the original drug.

How does trastuzumab work?

Some breast and stomach cancers have large amounts of human epidermal growth factor receptor 2 (HER2). They are called HER2 positive cancers. HER2 makes the cancer cells grow and divide.

Trastuzumab is a type of targeted cancer drug called a monoclonal antibody. It works by attaching to HER2 so it stops the cancer cells from growing and dividing.

Diagram showing a monoclonal antibody attached to a cancer cell

How do you have trastuzumab?

For breast cancer, you might have trastuzumab as a drip into your bloodstream (intravenously) or as an injection under the skin (subcutaneous). If you have trastuzumab intravenously, you may be able to switch to the subcutaneous injection.  

For stomach cancer, or gastro oesophageal junction cancer, you usually have trastuzumab as a drip into your bloodstream. 

Into your bloodstream

Each treatment takes between 30 and 90 minutes. You have the first treatment over 90 minutes and your team will check you for any side effects. Depending on the effects you have, the next infusion might be shorter.

You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:

  • central line
  • PICC line
  • portacath

If you don't have a central line, you might have treatment through a thin short tube (a cannula) that goes into a vein in your arm each time you have treatment.

As an injection under the skin

You might have trastuzumab as an injection under the skin, on the upper, outer part of your leg. The injection takes about 2 to 5 minutes.

It is important that your nurse changes which leg you have your injection in each time, to stop the area getting sore. They will check you for side effects for a few hours after the injection.

How often do you have trastuzumab?

For early breast cancer

You might have trastuzumab alone, or together with chemotherapy. You have it before or after surgery and chemotherapy. You usually have it every week (weekly regimen) or every 3 weeks (3 weekly regimen). This continues for up to a year. 

For advanced breast cancer 

As the first treatment for breast cancer that has spread, you might have it together with the chemotherapy drugs paclitaxel (Taxol) or docetaxel (Taxotere) or with hormone therapies called aromatase inhibitors. Open a glossary item

Trastuzumab is also used as a treatment on its own for people who have had at least 2 types of chemotherapy and where hormone therapy has not worked.

You have it every 3 weeks for as long as it is working and the side effects aren’t too bad.

For advanced stomach or gastro oesophageal cancer 

You might have trastuzumab as the first treatment for a type of stomach cancer called adenocarcinoma of the stomach that has spread to other parts of the body. Or for advanced gastro oesophageal junction cancer.

For stomach and gastro oesophageal junction cancer you usually have it together with the chemotherapy drug capecitabine (Xeloda). Or with the drugs fluorouracil and cisplatin. 

You usually have the combination of the drugs for the first 6 cycles of your treatment. A cycle is the time between one round of treatment until the start of the next.

After each round of treatment you have a break, to allow your body to recover

You then have trastuzumab alone for the remaining cycles.

You have it every 3 weeks for as long as it’s working, and the side effects aren’t too bad. 


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

You will also have a heart trace test (ECG) and a heart scan Open a glossary item before you start your treatment. You will have heart tests every few months while you are having trastuzumab and for some time after.

What are the side effects of trastuzumab?

How often and how severe the side effects are can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 
  • your side effects aren’t getting any better
  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Risk of infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 


You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

Bruising and bleeding

This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs (known as petechiae).

Allergic reaction

This usually happens with the first or second treatment. Symptoms include a skin rash, itching, feeling hot and shivering. Other symptoms include redness of the face, dizziness, a headache, shortness of breath and anxiety.

Pain in different parts of the body

You might feel some pain in different areas of your body. Most commonly from your muscles and joints. Other less common sites of pain include your bones, back, neck, arms and legs.

Speak to your doctor or nurse about what painkillers you can take to help with this.

You might have chest pain. If this pain is very severe, you should call 999

Diarrhoea or constipation

Tell your healthcare team if you have diarrhoea or constipation. They can give you medicine to help. 

Muscle spasms

Talk to your team about this.

Burning or tingling feeling in hands or feet

This might feel like itching or skin crawling. This is called paraesthesia.

Hot flushes or sweats

We have some tips for coping with hot flushes in women and hot flushes in men. This information also includes some of the possible treatments. Talk to your doctor if your hot flushes are hard to cope with. They might be able to prescribe you some medicines.


Contact your doctor or pharmacist if you have indigestion or heartburn. They can prescribe medicines to help.

Heart problems

You might get heart problems such as a change in your heart rhythm. Less commonly their   might be changes to the heart muscle not allowing it to pump blood around the body properly. You might also get fluid around the heart (called pericardial effusion), but this is rare.

You will have regular heart checks during and after treatment. Tell your doctor or nurse straight away if you have any chest pain.


Tiredness and weakness (fatigue) can happen during and after treatment. Doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.

Skin and nail problems

Skin and nail problems include a skin rash, dry skin, itching and darker skin. Your nails may also become brittle, dry, change colour or develop ridges. This usually goes back to normal when you finish treatment.

Occasionally you might have patches of discoloration from bleeding under the skin (called ecchymosis). Red pimples on the face (acne) can also be a side effect. Rarely, you might have red raised patches on your skin (called welts).

Mouth sores and ulcers

Mouth sores and ulcers can be painful. It helps to keep your mouth and teeth clean, drink plenty of fluids and avoid acidic foods such as lemons. Chewing gum can help to keep the mouth moist. Tell your doctor or nurse if you have ulcers.

Soreness, redness and peeling on hands and feet

The skin on your hands and feet may become sore, red, or may peel. You may also have tingling, numbness, pain and dryness. This is called hand-foot syndrome or palmar plantar syndrome.

Moisturise your skin regularly. Your healthcare team will tell you what moisturiser to use.

Taste changes

Taste changes may make you go off certain foods and drinks. You may also find that some foods taste different from usual or that you prefer to eat spicier foods. Your taste gradually returns to normal a few weeks after your treatment finishes.

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 

Blood pressure changes

During treatment, your blood pressure may be lower or higher than normal. Tell your nurse if you feel dizzy, faint, or if you have headaches, nosebleeds, blurred or double vision, or shortness of breath. Your blood pressure usually goes back to normal while you are on treatment or when treatment ends.

Eye problems

You might have eye problems including blurred vision, sore, red, itchy, dry eyes (conjunctivitis) or an infection. Tell your healthcare team if you have this. They can give you eye drops or other medication to help. 


You might feel like you are shaking or have tremors. 

Headaches and dizziness

Let your doctor or nurse know if you have headaches. They can give you painkillers. Don’t drive or operate machinery if you feel dizzy.

Swollen hands and feet

You may have swelling of your hands and legs due to a build up of fluid (oedema). 

Loss of appetite and weight changes

You might lose your appetite for various reasons when you are having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.

You might also lose or gain weight.

Difficulty sleeping

It can help to change a few things about how you try to sleep. Try to go to bed and get up at the same time each day and spend some time relaxing before you go to bed. Some light exercise each day may also help. 

Lung problems

This drug can cause you to develop a cough or shortness of breath. Less commonly this could be due to infection, such as pneumonia or lung problems such as asthma or a build up of fluid around the heart (pleural effusion). More rarely it might be due to inflammation of the lungs (pneumonitis) or scarring of the lungs. 

Let your doctor or nurse know straight away if you suddenly become breathless or develop a cough.

A runny nose

You might have a runny nose while having treatment.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. Avoiding fatty or fried foods, eating small meals and snacks, drinking plenty of water, and relaxation techniques can all help.

It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treating it once it has started.

Hair loss or thinning

Your hair may thin but you’re unlikely to lose all your hair. This usually starts after your first or second cycle of treatment. It is almost always temporary and your hair will grow back when you finish your treatment.

Flu like symptoms

This can happen a few hours after treatment. It may include headaches, muscle aches (myalgia), a high temperature and shivering. Taking paracetamol every 6 to 8 hours can help.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • feeling anxious or very low (depressed)
  • changes to the way your kidneys work - you have regular blood tests to check for this
  • liver problems that are very mild and unlikely to cause symptoms. Rarely you might have yellowing of the skin or whites of the eyes (jaundice)
  • dry mouth
  • stiff arms or legs
  • difficulty staying awake (drowsiness)
  • sweating more than normal for you
  • swollen or sore breasts
  • feeling generally unwell (malaise)
  • widening of your blood vessels that can make you feel weak, lightheaded, dizzy, faint and confused
  • piles (haemorrhoids)

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do I need to know?

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 7 months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner falls pregnant while having treatment.


You may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.    


Don’t breastfeed during this treatment and for 7 months afterwards. The drug may come through in the breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment. For example, if you need treatment for anything else, including teeth problems.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and one of the shingles vaccines called Zostavax.

You can have:

  • other vaccines, but they might not give you as much protection as usual
  • the flu vaccine (as an injection)
  • the coronavirus (COVID-19) vaccine - talk to your doctor or pharmacist about the best time to have it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

  • Electronic Medicines Compendium (eMC)

    Accessed April 2021

  • EPAR summary for the public - Herceptin (trastuzumab)
    European Medicines Agency, 2013

  • Breast Pathway Group – Subcutaneous Trastuzumab in Early Stage Breast Cancer

    London Cancer Alliance West and South, 2015

  • Breast Pathway Group – Intravenous Trastuzumab in Advanced Breast Cancer

    London Cancer Alliance West and South, 2016

  • Immunisation against infectious disease: Chapter 6: General contraindications to vaccination
    Public Health England
    First published: March 2013 and regularly updated on the Gov.UK website

Last reviewed: 
16 Apr 2021
Next review due: 
16 Apr 2024

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