Cancer drugs A to Z list
Phesgo is the name of an injection that contains both trastuzumab and pertuzumab. It is a type of targeted cancer drug. You pronounce Phesgo as fes-goh. You pronounce trastuzumab as tras-too-zoo-mab and pertuzumab as per-too-zoo-mab.
Phesgo is a treatment for breast cancer.
You can only have this medicine if your breast cancer is positive. You have tests on your breast cancer cells to check this.
You usually have Phesgo with .
Find out more about targeted treatment for breast cancer
You might have trastuzumab and pertuzumab as separate drugs. This page is about having the injection Phesgo that contains trastuzumab and pertuzumab.
Go to information about trastuzumab and pertuzumab
Phesgo is a combination of two targeted cancer drugs, trastuzumab and pertuzumab. These drugs are types of . Monoclonal antibodies work by attaching to specific proteins on the surface of cancer cells.
One of these proteins is called human epidermal growth factor receptor 2 (HER2). HER2 helps cells grow and divide. Some breast cancers have large amounts of HER2 on their surface. These are called HER2‑positive cancers.
Trastuzumab and pertuzumab attach to HER2 on the cancer cells. This helps to slow down or stop the cancer cells from growing and dividing. They may also help the body to destroy the cancer cells. Phesgo only works if your cancer is HER2 positive.
Find out more about monoclonal antibodies and how they work
You have Phesgo as cycles of treatment. This means that you have the drug and then a rest to allow your body to recover. You have Phesgo once every 3 weeks (21 days).
There are several different ways of having this treatment. Exactly how you have the Phesgo depends on your situation. Your doctor, nurse or pharmacist will tell you more about your treatment plan before you start.
The first injection of Phesgo is called the loading dose. It takes around 8 minutes. You stay for at least 30 minutes after this injection to check you have not had a reaction.
The second and future injections are called maintenance doses. These contain a smaller amount of the targeted drugs. This injection takes around 5 minutes. You stay for at least 15 minutes after each of these injections to check you have not had a reaction.
You have blood tests before and during your treatment. They check your levels of and other substances in the blood. They also check how well your liver and kidneys are working.
Before treatment starts you may have a blood test to check for viruses such as hepatitis B, hepatitis C, and HIV. This is called a viral screen.
It’s important for your doctor to know if you have had any of these viruses. This is because this treatment can weaken your and can cause the virus to become active again (reactivation).
Phesgo can affect how well your heart works. You usually have heart tests such as an before you start treatment and at different times throughout treatment.
Side effects can vary from person to person. They also depend on what other treatments you're having.
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.
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 is due to a drop in . 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.
You might be breathless and look pale due to a drop in . This is called anaemia.
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.
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 , 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 . 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.
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 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.
You might have pain in different areas of your body, most commonly from your muscles and joints. Other less common sites of pain include your arms, legs and tummy (abdomen).
Speak to your doctor or nurse if you are in pain as they can figure out the cause and give medicines to help.
You might have skin problems such as a skin rash or dry skin.
Less common skin problems include itching. Your nails may also become brittle, dry, change colour or develop ridges. You might have inflammation of the nail bed where your nail and skin meet. This usually goes back to normal when you finish treatment.
Let your healthcare team know of any skin and nail changes. They might be able to give you medicine to help.
You might lose your appetite for various reasons while having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.
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.
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 if needed.
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.
Contact your doctor or pharmacist if you have indigestion or heartburn. They can prescribe medicines to help.
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.
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.
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.
Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.
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.
You might have nose bleeds while having treatment. Speak to your nurse if this happens to you.
This treatment may cause of the . You might have soreness or pain in your throat, abdomen and back passage (rectum). Let your nurse or pharmacist know if you have this.
Phesgo commonly causes a cough. Less commonly you may notice you are short of breath. Phesgo can also cause changes to your lung tissue causing inflammation, stiffness and scarring. It is not known how often this happens. This can make it difficult to breathe. Symptoms can include shortness of breath, chest pain, a dry cough and changes to your breathing.
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:
dizziness
watery eyes
heart problems – symptoms can include feeling tired, a cough that doesn’t go away, breathlessness, swelling in legs, ankles or tummy (abdomen)
a high temperature
fluid build up in in your arms, hands, ankles, or legs (oedema)
a cold – symptoms include a runny or blocked nose, sore throat, sneezing, cough, high temperature and generally feeling unwell
You might have an allergic reaction with this treatment. This happens in fewer than 1 in 100 people (less than 1%).
Symptoms include a skin rash, shortness of breath, redness or swelling of the face or throat and dizziness. Some allergic reactions can be life threatening. Alert your nurse or doctor if notice any of these symptoms.
This is a new drug in cancer treatment. So there is limited information available at the moment about possible rare and longer term effects that it may cause. Tell your doctor if you notice anything that is not normal for you.
This treatment can cause , but there isn't enough information to work out how often this side effect might happen.
Cytokines are a group of proteins in the body that play an important part in boosting the . This treatment stimulates the immune system to make large amounts of cytokines. This can cause symptoms which can be severe. Some of the symptoms include fever, chills, a headache, difficulty breathing, and dizziness.
We have more information about side effects and tips on how to cope with them.
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.
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 after treatment.
Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner becomes pregnant while having treatment.
It is not known whether this treatment affects 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.
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, 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.
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 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.
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 and Healthcare products Regulatory Agency (MHRA) as part of their Yellow Card Scheme.
Last reviewed: 02 Jul 2026
Next review due: 02 Jul 2029
Targeted cancer drugs work by targeting the differences in cancer cells that help them to grow and survive. Immunotherapy uses our immune system to fight cancer.
Monoclonal antibodies (mAbs) are a type of cancer treatment. They may be called a type of targeted cancer drug or immunotherapy. But they can work in both ways. Find out more.
Cancer drugs have side effects and these can vary from person to person. But there are things that you can do to help you cope.
Coping with cancer can be difficult. There is help and support available. Find out about the emotional, physical and practical effects of cancer and how to manage them.
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