Trastuzumab and pertuzumab

Trastuzumab and pertuzumab are types of targeted cancer drugs. You might have them on their own or with other chemotherapy drugs.

It is a treatment for breast cancer.

How they work

Trastuzumab and pertuzumab are types of targeted cancer drugs called monoclonal antibodies. Monoclonal antibodies work by attaching to proteins on or in cancer cells.

Human epidermal growth factor 2 (HER2) is a protein that makes cells grow and divide. Some cancers have large amounts of HER2 protein and are called HER2 positive cancers. These drugs work by locking onto HER2 on the cancer cells. The aim is to stop the cells them from growing and kills them.

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

How you have them

You have trastuzumab and pertuzumab into your bloodstream (intravenously) or as an injection under your skin (subcutaneously).

Into your bloodstream 

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. You have a new cannula each time you have treatment.

As an injection under your skin

The combination of trastuzumab and pertuzumab as an injection under your skin is called Phesgo. Having these drugs this way is quicker than having them into your bloodstream. You usually have these every 3 weeks.

Your doctor will let you know if this is suitable for you and how many treatments you will have.

Your first injection is called a loading dose. This means you have a large amount once only. For your second and future injections, you have a smaller amount. This is called a maintenance dose.

You usually have the injection in your thigh. With each dose, your nurse will vary the site where you have it. For example, you have one dose in your right thigh and the next in your left.

When you have them

You have trastuzumab and pertuzumab as a course of several cycles of treatment. This means that you have the drugs and then a rest to allow your body to recover. Each cycle of treatment is usually 3 weeks, although this might vary depending on your individual treatment.

The number of cycles you have depends on if you have them alone or with chemotherapy drugs. Your healthcare team will go through your treatment plan with you before you start.


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.

Side effects

We haven't listed all the side effects. It is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

How often and how severe the side effects are can vary from person to person. They also depend on what other treatment you are having. For example, your side effects could be worse if you are also having other drugs.

When to contact your team

Your doctor or nurse will go through the possible side effects. They will monitor you closely 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 doctor or nurse immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

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:

Increased risk of getting an 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. 

Breathlessness and looking pale

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

Bruising, bleeding gums or nose bleeds

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).


Pertuzumab can cause severe diarrhoea that can make you dehydrated and poorly. Contact your advice line or healthcare team when this starts. 

Your doctor may give you anti diarrhoea medicine to take home with you after treatment. Eat less fibre, avoid raw fruits, fruit juice, cereals and vegetables, and drink plenty to replace the fluid lost.

Tiredness and weakness (fatigue)

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

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.

Pain in your body, muscle and joints

You might feel some pain from your body, muscles and joints. Speak to your doctor or nurse about what painkillers you can take to help with this.

Skin and nail problems

Skin and nail problems include a skin rash, dry, 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.

Rarely, you might develop a raised, red, itchy rash which looks like a nettle rash. This is known as hives. Let your healthcare team know if this happens as you might be able to have medicine to help. 

Soreness, redness and peeling on palms and soles of 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.

Loss of appetite and weight loss

You might not feel like eating and may lose weight. It is important to eat as much as you can. Eating several small meals and snacks throughout the day can be easier to manage. You can talk to a dietitian if you are concerned about your appetite or weight loss. 

Sore mouth

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.


Constipation is easier to sort out if you treat it early. Drink plenty of fluids and eat as much fresh fruit and vegetables as you can. Try to take gentle exercise, such as walking. Tell your doctor, nurse or pharmacist if you are constipated for more than 3 days. They can prescribe a laxative.

Difficulty sleeping (insomnia)

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. 

Indigestion or heartburn

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

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.

Fluid build up

A build up of fluid may cause swelling in your arms, hands, ankles, legs, face and other parts of the body. Contact your healthcare team if this happens to you.

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. 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.

Hair loss

You could lose all your hair. This includes your eyelashes, eyebrows, underarms, legs and sometimes pubic hair. Your hair will usually grow back once treatment has finished but it is likely to be softer. It may grow back a different colour or be curlier than before. 

Flu-like symptoms

You may have headaches, muscle aches (myalgia), a high temperature and shivering. You should contact your advice line urgently if you have these symptoms.

Numbness or tingling in fingers or toes

Numbness or tingling in fingers or toes 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. 

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. 

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.

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.

Heart problems

This includes your blood pressure being lower or higher than normal. This can make you feel dizzy, faint, or you might have headaches, nosebleeds, blurred or double vision, or shortness of breath.

Other heart problems include changes in your heart rhythm such as an irregular heartbeat or palpitations.

Less commonly your heart muscle might stop working properly. This can make you feel confused, dizzy and faint, you might have a persistent cough that gets worse at night, a wheeze and fast heart rate.

Rarely, you might get a build up of fluid around the heart. This can cause swelling in your legs or tummy, chest pain, and shortness of breath.

You may have regular heart tests such as an ECG Open a glossary item to check your heart function. 

Tell your doctor or nurse straight away if you have any of these symptoms.

Runny nose

You might have a runny nose while having treatment.

Shaky hands (tremor)

You may develop shaky hands (tremor) with this treatment.

Shortness of breath, wheeze or a cough

These drugs can cause lung problems.

Rarely, pertuzumab can cause changes to your lung tissue which makes it stiff and leaves scarring. This can make it difficult to breathe. You can also get a build of fluid in the lungs causing chest pain, a dry cough, and changes to your breathing.

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

Inflammation around the injection site

You might notice pain, bruising, or sore skin around the area where you have had the injection. 

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, very low in mood (depressed) and not thinking straight
  • feeling very sleepy
  • unable to control your body movements (ataxia)
  • the muscles in your body might get stiff so you find it difficult to move (hypertonia)
  • swollen veins near your anus (piles or haemorrhoids) – this can be painful when you have a poo – let your team know if you have this
  • dry mouth
  • excessive sweating
  • changes to the way your kidneys work – you have regular blood tests to check this
  • swelling of your one or both breasts
  • feeling generally unwell

Rare Side effects

These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:

  • high levels of chemicals in your blood due to the breakdown of tumour cells (tumour lysis syndrome) - you have regular blood tests to check for this
  • cytokine release syndrome, this is where the drugs stimulate the immune system to make large amounts of a group of proteins called cytokines. Symptoms include high temperature, chills, headache, difficulty breathing and dizziness

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.

Loss of fertility

It is not known whether this treatment affects fertility 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 because the drug may come through into your breast milk and for 7 months after your last treatment.

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.

Related links