Phesgo or trastuzumab and pertuzumab

Trastuzumab and pertuzumab are 2 cancer drugs given together. It’s used to treat early, ​locally advanced​ and ​secondary breast cancer​ that is HER2 positive.  

You pronounce trastuzumab as tras-too-zoo-mab and pertuzumab as per- too-zoo-mab. 

You might have a combined treatment of these 2 drugs called Phesgo (pronounced fes-goh).

Trastuzumab, pertuzumab and Phesgo are types of targeted cancer drugs. You might have them with ​chemotherapy​ drugs.

Find out more about breast cancer and its treatment

How does Phesgo or trastuzumab and pertuzumab work?

Phesgo, 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. They are called HER2 positive cancers. 

These drugs work by locking onto HER2 on the cancer cells. The aim is to stop the cells from growing and kills them. They only work if your cancer is HER2 positive. You have tests on your cancer cells to check for this.

Find out more about monoclonal antibodies and how they work

How do you have Phesgo or trastuzumab and pertuzumab?

You have:

• pertuzumab into your bloodstream (intravenously)

• trastuzumab can be given intravenously or as an injection under the skin (subcutaneously) 

• Phesgo is given as an injection under your skin

As an injection under your skin

The most common way to have trastuzumab and pertuzumab is a combination of both drugs called Phesgo as an injection. You usually have this every 3 weeks.

Your first injection is called a loading dose. This means you have a large amount once only. It takes around 8 minutes. For your second and future injections, you have a smaller amount. This is called a maintenance dose which takes around 5 minutes.  

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. 

Your doctor or pharmacist will let you know how many treatments you will have.

Into your bloodstream

You might have trastuzumab and pertuzumab 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.

How long does each treatment take?

Having trastuzumab and pertuzumab or Phesgo can take between 30 minutes to 6 hours for your first dose. This depends on:

• what treatment you have

• how you have it - intravenously or as an injection under your skin

The time includes your treatment and observation time. This means you stay in the department after you finish your treatment. Your nurse checks you regularly for possible side effects.

Your second and subsequent treatments are usually shorter.  

Your nurse or pharmacist will tell you about your treatment. And how long you need to stay for observation afterwards.

How often do you have Phesgo or trastuzumab and pertuzumab?

Early and locally advanced breast cancer 

You usually have trastuzumab and pertuzumab or Phesgo every 3 weeks. You have it with chemotherapy for several cycles then continue having it on its own. You might have this treatment for up to 1 year as long as it's working and the side effects aren’t too bad.

You might have this treatment with chemotherapy before surgery and continue afterwards.

Secondary breast cancer 

If you have secondary breast cancer you usually have this treatment every 3 weeks with a chemotherapy drug called docetaxel. Or you might have a different chemotherapy called paclitaxel, which you have weekly. You then continue having it after you finish your course of chemotherapy. And continue taking it on its own as long as it's working and the side effects aren’t too bad. 

Your healthcare team will tell you about your treatment plan before you start.

Tests

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, pertuzumab, and Phesgo can affect how well your heart works. You usually have tests to measure your heart function. For example, you might have an ​echocardiogram​  (ECHO) or a ​MUGA​ scan before you start your treatment and usually at different times throughout. This depends on the results of the test you have and the symptoms you may have.

Your doctor or pharmacist will tell you more about these tests and how often you have them.

Find out about these tests in our A-Z list

What are the side effects?

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. 

We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.

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:

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, cough, headaches, feeling cold and shivery, pain or a burning feeling when peeing, or generally feeling 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. This is known as petechiae.

Allergic reaction

A reaction may happen during the infusion. Symptoms can include a skin rash, itching, swelling of the lips, face or throat, breathing difficulties, fever and chills. Your nurse will give you medicines beforehand to try to prevent a reaction. 

Inflammation around the injection site

You might notice pain, bruising, or sore skin around the area where you have had the injection. Let your nurse know straight away if this happens. 

Diarrhoea

Contact your advice line if you have diarrhoea. For example, in one day you have 2 or more loose bowel movements than usual. If you have a ​stoma​ , you might have more output than normal. Your doctor may give you anti diarrhoea medicine to take home with you after treatment.

Try to eat small meals and snacks regularly. It’s best to try to have a healthy balanced diet if you can. You don’t necessarily need to stop eating foods that contain fibre. But if your diet is normally very high in fibre, it might help to cut back on high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables. 

Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.

Heart problems and blood pressure changes

You might have heart problems such as a change in your heart rhythm. This treatment can also cause changes to the heart muscle. This can sometimes cause problems pumping blood around the body properly. 

You might also get fluid around the heart (pericardial effusion), but this is rare. Symptoms can include:

• a faster heartbeat

• shortness of breath

• feeling tired and dizzy

You might have regular heart tests such as an ECG to check your heart function. 

This treatment can cause chest pain - call 999 if you have chest pain. 

Trastuzumab can cause changes in your blood pressure. It 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.

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. 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.

Pain in your body, muscles and joints

You might have pain in different areas of your body. Most commonly from your muscles and joints and in your tummy (abdomen). Or you might have muscle spasms and your muscles can feel stiff but this isn’t very common. 

Other less common sites of pain include your bones, back, neck, arms and legs. Speak to your doctor or nurse about pain relief tablets or other treatments that may help relieve the pain.

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.

Occasionally you might have patches of discoloration from bleeding under the skin. Or you may have general inflammation of the skin (dermatitis). Red pimples on the face (acne) can also be a side effect. 

Rarely, you might have red raised patches on your skin. Or you might get an infection in your nails. This can cause redness, pain and tenderness around the nail. You might have a condition where your nails separate from the nail bed but this is also rare.

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

You might not feel like eating and may lose weight. 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 your mouth moist. Tell your doctor or nurse if you have ulcers.

Constipation

​Constipation​ is easier to sort out if you treat it early. Drink plenty and eat as much fresh fruit and vegetables as you can. Try to take gentle exercise, such as walking. Tell your healthcare team if you think you are constipated. They can give you a laxative if needed.

Difficulty sleeping (insomnia)

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. 

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.

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. 

Cold and 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 medicines 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 some medicines to help.

Runny nose and nose bleeds 

You might have a runny nose or nose bleeds while having treatment. Speak to your nurse if this happens to you. 

Inflammation of the digestive system

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

Shaky hands

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

Problems with your lungs - shortness of breath, wheezing or a cough

These drugs can cause lung problems including shortness of breath and coughing. Less commonly you may notice you are wheezing or you might develop a chest infection. Symptoms include a high temperature, difficulty breathing, headaches and feeling weak with muscle aches.

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

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 in mood (depressed)

• feeling very sleepy

• 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

• changes to the way your kidneys work - you have regular blood tests to check this

• feeling generally unwell

• swollen or sore breasts

• 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

• widening of your blood vessels that can make you feel weak, lightheaded, dizzy, faint and confused

• sweating more than normal for you

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

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 this treatment 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.

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.

Breastfeeding

Don’t breastfeed during this treatment and for 7 months after your last treatment. This is because the drug may come through into your 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.

Immunisations

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, and yellow fever.

You can usually 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 a vaccine in relation to your cancer treatment.

Contact with others who have had immunisations 

You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your ​immune system​ is weakened.

Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.

Read more about immunisations and cancer treatment