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Subcutaneous Trastuzumab and Pertuzumab  (Phesgo®)

Information leaflet on SUBCUTANEOUS Trastuzumab and Pertuzumab  (Phesgo®) for breast cancer patients A1349

This leaflet provides information for patients having treatment with the drugs Trastuzumab and Pertuzumab (Phesgo®).   The leaflet will explain:

  • what Phesgo® is
  • when and how it is given
  • common side effects that you may experience

Your ‘specialist team’ refers to your Oncology Team at Velindre Cancer Centre which includes Doctors, Specialist Nurses and Non-medical Independent Prescribers which may be a Nurse or a Pharmacist. 

What is Phesgo® and why am I having it?

Your cancer showed a high level of a protein (receptor) known as HER2 (Human Epidermal growth Receptor- factor 2).  HER2 is found on the outside of some cancer cells and it stimulates their growth.

Phesgo® belongs to a group of cancer drugs called monoclonal antibodies. Monoclonal antibodies are sometimes called targeted therapies because they work by ‘targeting’ specific proteins (receptors) on the surface of cells.  Phesgo® locks onto the HER2 protein.  This blocks the receptor and stops the cells from dividing and growing.

How often will I receive Phesgo ®?

Phesgo® is given once every 3 weeks.  
Your Team will explain how many injections you will have.

How is Phesgo® given?

Phesgo® is given by subcutaneous injection under the skin on your thigh.  The administration of Phesgo® by subcutaneous injection will take between 5-8 minutes.  The injection site will change from your left to right thigh each treatment cycle.  In order for the Nurse to give the injection into your leg it is advisable to wear comfortable loose-fitting clothing, for example a skirt or trousers, to enable access to your thigh for administration on the day of your treatment.

How often will I see the specialist team?

You may be reviewed by your team.  Your Team will tell you how often they will review you.  They will review you regularly, you will either see them in clinic or you will speak to them over the telephone or by video.  This is so we can check how the treatment is affecting you.  

Where do I receive my treatment?

The treatment will be administered in one of the day case treatment areas at Velindre Cancer Centre (VCC), or in one of the VCC outreach Units.

Can I bring relatives and friends with me? 

You are welcome to bring someone to stay with you during your treatment. Space is limited so there is not usually room for more than one person.  Treatment areas are not suitable for young children.

How long will my appointment take?

Your first appointment will take approximately 1 hour as you will be required to be observed after your first injection for 30 minutes.  Your appointments after cycle 1 should take approximately 45 minutes.

Side effects during the treatment

Most people tolerate Phesgo® treatment very well, with very few side effects.  However, as with all drugs, there are a number of known side effects which can occur.  Some of these are detailed below, your Team can give you advice or answer any questions you may have.  

Most side effects which can occur with Phesgo® occur at the time the drug is given.  A Nurse will monitor you closely during the treatment.

If you experience any of the following during the treatment or immediately after treatment please tell your Nurse straight away:

  • Feeling hot and feverish
  • Chills or shivering
  • Headache
  • Dizziness or faintness
  • Problems with breathing
  • Rash
  • Feeling sick or vomiting.

Other common side effects you may experience in the first few days after treatment include:

  • Diarrhoea
  • Weakness
  • Fatigue
  • Skin rashes
  • Abdominal pain
  • Joint pain
  • Muscle pain
  • Hot flushes
  • Pain at the injection site.

These side effects usually only last a few days.  Taking a mild painkiller, for example whatever you usually take for a headache, may help.  If you feel very unwell or want further advice please contact the Velindre Cancer Centre Treatment Helpline. The number is at the end of the leaflet

Heart problems

Phesgo® treatment may cause some heart problems.  This is rare and the risk of developing serious heart problems is less than 1%.  Any problems which are caused by Phesgo® will usually get better when the completed treatment cycles have finished.  Your Team will discuss this with you and arrange for your heart function to be tested before you start Phesgo®.  Your heart function will be monitored usually every 4 months for the first year of treatment.  We will also check your blood pressure and monitor your weight regularly.

If you already have a heart condition or you take any heart medication, please tell your Velindre Oncology Team before you start treatment with Phesgo®.  If you do develop heart problems whilst on Phesgo® it can be treated with tablets.  It is very important not to stop taking any tablets you have been given for heart problems without discussing it with your Team

If at any time during your treatment you become breathless, develop a cough, experience fluid retention (swelling) in your arms or legs, or palpitations (heart flutter or irregular heart beat) please contact the Velindre Cancer Centre Treatment Helpline immediately.

Anaemia and low platelets 

If you feel tired, short of breath or notice excessive bruising or bleeding, ring the treatment helpline.  

Is it ok to take other medication with Phesgo®?

It is important you tell your Oncology Team medication which you are take and that you continue to take them.

Phesgo® can remain in your body for up to 6 months after you finish treatment.  During this time you should tell your Doctor and Pharmacist that you have had Phesgo® before starting any new medicines.

Who do I contact if I am unwell during my Phesgo® treatment?

If you are unwell at home and need advice at any time of the day or night phone Velindre Cancer Centre 029 2061 5888 and ask for the Treatment Helpline

Sometimes cancer drugs can have very serious side effects which can be life threatening. It is important to inform Velindre Cancer Centre if you are concerned about any side-effects

Other information

It is important you do not become pregnant whilst on Phesgo® or for 7 months after your treatment is completed.

Breastfeeding is not recommended whilst on Phesgo®.

Manufacturer’s patient information leaflets 

This leaflet was written by Velindre Cancer Centre healthcare professionals in line with the Velindre Cancer Centre Protocol. The information contained in this leaflet is evidence based. The leaflet has been approved by a Velindre Cancer Centre group of Doctors, Nurses, Pharmacists and Patient Representatives. It will be reviewed and updated every 2 years.

Copies of the drug manufacturer’s patient information leaflets are available from the Velindre Pharmacy, your treatment centre or on the internet at These leaflets provide detailed information on individual drugs. We don’t give them out routinely as they can be difficult to read. Please ask if you would like a copy.

Contact telephone numbers

Velindre Cancer Centre 029 2061 5888
Ask for the Treatment Helpline if you are unwell at home and need immediate attention at any time of the day or night. 

Pharmacy department 029 2061 5888 ext 6223
Monday – Friday 9am – 5pm for queries about your medicines

Tenovus freephone 0808 808 1010
Cancer Helpline 

This information is also available in Welsh.