Trastuzumab is a targeted cancer drug. You pronounce it as tras-too-zoo-mab. It’s also known by other names such as Herceptin, Herzuma and Ontruzant.

Trastuzumab is a treatment for:

  • breast cancer – for early breast cancer Open a glossary item, locally advanced breast cancer Open a glossary item and secondary breast cancer Open a glossary item
  • advanced stomach cancer  
  • advanced cancer of where the food pipe joins your stomach (gastro oesophageal junction)

How does trastuzumab work?

Trastuzumab is a type of targeted cancer drug called a monoclonal antibody. Targeted cancer drugs work by ‘targeting’ those differences that help a cancer cell to survive and grow. It is a treatment for cancers that have large amounts of a protein called human epidermal growth factor receptor 2 (HER2).

Human epidermal growth factor 2 (HER2) is a protein that makes cells grow and divide.

Diagram showing a monoclonal antibody attached to a cancer cell

Some breast and stomach cancers have large amounts of HER2 protein. These are called HER2 positive cancers. Trastuzumab works by locking onto HER2 on the cancer cells. The aim is to stop the cells from growing and kills them.

Trastuzumab only works if your cancer is HER2 positive. You have tests on your cancer cells to check for this. 

You might have the original drug called Herceptin, or a biosimilar. A biosimilar is a very similar copy of the original drug, but it is not exactly the same. There are various biosimilar brands of this drug.

Biosimilars undergo strict testing to check they work just as well as the original drug.

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).

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 healthcare 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

If you have trastuzumab to treat breast cancer you might have it 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. This helps to stop the area from getting sore. They will check you for side effects for a while after the injection. 

You may have trastuzumab in combination with other drugs.

How often do you have trastuzumab?

Trastuzumab for early breast cancer

You usually have trastuzumab every three weeks for early breast cancer. You might have it on its own or together with chemotherapy before or after surgery. If you have trastuzumab before your surgery you usually continue having it afterwards. This can be up to one year.

Trastuzumab for locally advanced breast cancer

You usually have trastuzumab with chemotherapy every 3 weeks. You continue to have it on its own after you finish your chemotherapy.

Trastuzumab for advanced breast cancer 

You usually have trastuzumab once every 3 weeks for advanced breast cancer. You might have it on its own if you’ve previously had chemotherapy and aromatase inhibitors Open a glossary item. Or you might have it with chemotherapy or aromatase inhibitors if this is your first treatment for advanced breast cancer. 

You have it for as long as it is working, and the side effects aren’t too bad. Your doctor and pharmacist will explain in more detail how often you have trastuzumab and other drug treatments you might have with it. 

Trastuzumab 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. 

You usually have trastuzumab together with chemotherapy. You might have cisplatin with fluorouracil or capecitabine. You usually have this for the first 6 cycles of your treatment Open a glossary item. You then have trastuzumab alone.

You usually continue to 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.

Trastuzumab can change the way your heart works. Before your treatment, you have tests to measure your heart function. For example, an echocardiogram Open a glossary item (ECHO) or a MUGA Open a glossary item scan. You also have these tests at different times throughout your treatment. You might continue to have them for a few months after your treatment finishes.

How often you have these tests depends on the results of the tests and your symptoms. Your doctor or pharmacist will tell you more about them. 

What are the side effects of trastuzumab?

Side effects 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.

The side effects listed are for trastuzumab on its own. The side effects you have may vary if you are having chemotherapy or other anti-cancer drugs with trastuzumab. 

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

A reaction may happen during the infusion, causing a skin rash, itching, swelling of the lips, face or throat, breathing difficulties, fever and chills.

Allergic reactions can sometimes be life threatening. Tell your nurse or doctor immediately if at any time you feel unwell. They will slow or stop your drip for a while and give you medicine to help relieve the side effects.

Heart problems

You might get heart problems such as a change in your heart rhythm. Or you might also have changes to the heart muscle. This can sometimes cause problems pumping blood around the body properly. This is usually if you have trastuzumab with some types of chemotherapy drugs.

This treatment can cause chest pain. If this pain is severe, call 999.

Some people on this treatment might get fluid around the heart (pericardial effusion), but this is rare. Symptoms can include a faster heartbeat, shortness of breath, and feeling tired and dizzy.

You will have regular heart checks before, during and after treatment. 

Diarrhoea or constipation

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

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, in your tummy (abdomen). Or you might have muscle spasms and your muscles can feel stiff but this isn’t very common.

This treatment can cause chest pain. If this pain is severe, call 999.

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.

Numbness or tingling feeling

You might have numbness or tingling (pins and needles) in your fingers or toes or other parts of your body. This is often temporary and can improve after you finish treatment. Tell your healthcare team if you're finding it difficult to walk or complete fiddly tasks such as doing up buttons. 

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 Open a glossary item or heartburn. They can prescribe medicines to help.


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 problems include a skin rash, dry skin and itching. 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. Or you may have general inflammation of the skin (dermatitis). Rarely, you might have red raised patches on your skin. 

Mouth sores and lip swelling

You might have mouth sores and ulcers that 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. Your lips can also become swollen with this treatment. And you might also have a dry mouth but this is less common.

Tell your doctor or nurse or pharmacist if you have pain or ulcers in your mouth.

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.

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, or an infection (conjunctivitis). Tell your healthcare team if you have these symptoms. 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.

General swelling

You may have swelling of your hands, legs, and face 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 weight with this treatment. Speak to your nurse if you are worried about weight loss.

Difficulty sleeping

If you have 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.

Nosebleeds or a runny nose

You might have a runny nose while having treatment or you might have nosebleeds.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also 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 treat it once it has started.

Hair loss or thinning

You could lose all your hair or it may become thinner. This includes your eyelashes, eyebrows, underarm, leg and sometimes pubic hair. It usually happens gradually within 2 to 3 weeks after the start of your treatment. 

Your hair usually grows back once your treatment has finished. This can take several months and your hair is likely to be softer. It can also grow back a different colour or be curlier than before.

Flu like symptoms

This can happen a few hours after treatment. It may include headaches, muscle aches (myalgia), a high temperature and shivering. Speak to your pharmacist or nurse about what you can take to help.

High temperature or chills

You might get a high temperature. Or you might feel cold or start shivering (chills). 

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

Inflammation of the digestive system

This treatment may cause inflammation of the digestive system Open a glossary item. You might have soreness or pain in your throat, tummy (stomach) and back passage (rectum).  Let your nurse or pharmacist know if you have this.

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 mild. You might have symptoms including tummy pain. Or yellowing of the skin or whites of the eyes (jaundice), but this is rare

  • difficulty staying awake (drowsiness)

  • sweating more than normal for you

  • swollen or sore breasts

  • feeling generally unwell

  • 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 medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant 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 become pregnant while having treatment.


It is not known whether this treatment affects fertility Open a glossary item in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.


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

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.


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 and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

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

Related links