1. What is trastuzumab?
2. How does trastuzumab work?
3. Who might be offered trastuzumab?
4. When is trastuzumab given?
5. How is trastuzumab given?
6. What happens if I miss a dose?
7. How long will I have trastuzumab for?
8. What are the possible side effects of trastuzumab?
9. Blood clots
10. Can I get pregnant or breastfeed while having trastuzumab?
11. Travel and vaccinations

1. What is trastuzumab?

Trastuzumab is a targeted (biological) therapy. Targeted therapies block the growth and spread of cancer. They target and interfere with processes in the cells that help cancer grow.

You may have a brand of trastuzumab called Herceptin. Alternatively you may have a drug with a different brand name such as Herzuma, Kanjinti or Ontruzant. These drugs are very similar to trastuzumab and work in the same way. You might hear them referred to as trastuzumab biosimilars, and more brands will be available in the future.

2. How does trastuzumab work?

Some breast cancer cells have a higher than normal level of a protein called HER2 on their surface, which stimulates them to grow. Around one in five invasive breast cancers (breast cancer that has the potential to spread to other parts of the body) have this and are called HER2 positive.

Trastuzumab works by attaching itself to the HER2 proteins so that the cancer cells are no longer stimulated to grow. It also helps the body’s immune system destroy breast cancer cells.

3. Who might be offered trastuzumab?

Only people with HER2 positive breast cancer will benefit from having trastuzumab. If your cancer is HER2 negative, then trastuzumab will not be of any benefit.

There are various tests to measure HER2 levels which are done on breast tissue removed during a biopsy or surgery.

HER2 testing is normally only done on invasive breast cancer (which has the potential to spread to other areas of the body), so it’s unlikely to be mentioned if you have an early form of breast cancer called ductal carcinoma in situ (DCIS).

Trastuzumab may not be suitable for people who have heart problems or high blood pressure (hypertension) that is not well controlled. If your breast cancer is HER2 positive and you have heart problems, your treatment team will usually arrange additional tests to check how well your heart is working.

4. When is trastuzumab given?

Primary breast cancer

Trastuzumab can be used as a treatment for primary breast cancer (breast cancer that has not spread beyond the breast or the lymph nodes under the arm).

Before surgery

Sometimes, trastuzumab is given before surgery. This is known as neo-adjuvant or primary therapy. It may be used to slow down the growth of breast cancer to reduce the chance of it spreading to other parts of the body, or to help shrink a large breast cancer before surgery. It may be given with chemotherapy, and sometimes with another drug called pertuzumab (Perjeta).

Your treatment team will be able to explain the reasons for recommending each treatment and when it will be given.

After surgery

It can be given after surgery to reduce the likelihood of the breast cancer returning or spreading to another part of the body. This is known as adjuvant treatment. It may be given with or after chemotherapy, and sometimes with pertuzumab.

Breast cancer recurrence

Trastuzumab may be used to treat breast cancer that has come back in the chest, breast or skin near the original site or scar (known as local recurrence).

Trastuzumab can also be used when the breast cancer has come back and spread to the tissues and lymph nodes around the chest, neck and under the breastbone (known as locally advanced or regional recurrence).

Secondary breast cancer

Trastuzumab can be used to treat secondary breast cancer. This is when cancer cells from the breast have spread to other parts of the body such as the bones, lungs, liver or brain.

5. How is trastuzumab given?

Trastuzumab can be given:

  • as a drip into a vein (intravenous infusion) in your arm or hand
  • as an injection into the fatty tissue under the skin (subcutaneous injection) in your thigh

It is most commonly given once every three weeks. Some people may have it weekly. You’ll usually have your treatment as an outpatient at the hospital, although some people are able to have their treatment at home.

Trastuzumab is usually given with chemotherapy because this is how it has been studied in clinical trials. It can also be given alongside other treatments such as radiotherapy, hormone therapy and another biological therapy called pertuzumab (Perjeta).

As a drip

The first infusion is usually given over an hour and a half. You will be asked to stay in the hospital for several hours after your treatment to ensure you’re not feeling unwell before leaving. If there are no problems, future doses can be given over 30 minutes and you’ll only need to stay for a couple of hours afterwards.

The drug may be given through a tube that’s put into the vein each time you have the treatment, or it may be given through a device that stays in place throughout the whole course of the treatment.

As an injection

This is given over two to five minutes. The injections are given into the right and left thighs alternately. You will be asked to stay in the hospital for a few hours after your first injection to make sure you’re not feeling unwell before leaving. If there are no problems you won’t need to stay as long after future doses.

If you are already having trastuzumab as an intravenous infusion you may be switched to the subcutaneous injection.

The trastuzumab biosimilars Herzuma, Kanjinti and Ontruzant are not available as a subcutaneous injection.

6. What happens if I miss a dose?

If you’re having trastuzumab over many months you may want to miss or delay one treatment, for example to take a holiday. If you want to do this, discuss it with your treatment team beforehand.

7. How long will I have trastuzumab for?

If you’re having trastuzumab to treat primary breast cancer after surgery it’s usually given for one year (around 18 cycles).

If you are having trastuzumab before surgery you will usually have four to six cycles.

If you’re having trastuzumab to treat secondary breast cancer it’s usually given for as long as it’s keeping the cancer under control.

8. What are the possible side effects of trastuzumab?

Like any treatment, trastuzumab can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. These side effects can usually be managed and those described here will not affect everyone.

If you’re concerned about any side effects, regardless of whether they are listed here, talk to your treatment team as soon as possible.

If you are being given chemotherapy and trastuzumab at the same time you may have other side effects from the chemotherapy.

Common side effects

Flu-like symptoms

Fever, chills and mild pain in some parts of the body can occur during or shortly after your treatment. These symptoms are more common the first time you have trastuzumab and don’t usually last long. Taking pain relief can help.

Nausea (feeling sick)

This is usually mild and doesn’t last long. Anti-sickness drugs can be prescribed to relieve it.


You may have mild diarrhoea. Your treatment team or GP can prescribe drugs to help control it. Contact your treatment team if you have four or more episodes of diarrhoea within 24 hours.

Soreness at the injection site

You may experience some soreness at the injection site if you have trastuzumab as a subcutaneous injection.

Less common side effects

After the first treatment you may have other side effects including:

  • headaches
  • dizziness
  • joint and muscle pain
  • rash
  • vomiting (being sick)
  • breathlessness

These side effects are often mild and don’t usually continue with future treatments.

Rarer side effects

Allergic reaction

If you have an allergic reaction to trastuzumab, it will probably happen within the first few hours after your treatment and will most likely be the first or second time you have the drug. Reactions can vary from mild to severe, but severe reactions are uncommon. You will be monitored closely during your treatment so that any reaction can be dealt with immediately.

Symptoms of an allergic reaction include flushing, skin rash, itching, back pain, shortness of breath, faintness, fever or chills. If you have a severe reaction, treatment will be stopped immediately.

Occasionally these symptoms start later than six hours after your treatment. If this happens contact your hospital immediately.

Heart problems

There is a small chance of developing heart problems such as an abnormal heart rhythm, which can cause symptoms such as breathlessness, discomfort in the chest or a feeling like your heart is racing.

Tests to check how well your heart is working, including an echocardiogram (an ultrasound of the heart) or multiple-gated acquisition (MUGA) scan (a scan that uses a small amount of radioactive material), are usually carried out before treatment starts.  

You may continue to have tests (usually an echocardiogram) every three months during treatment, and every six months for two years after your last dose of trastuzumab.

Heart problems are more likely when trastuzumab is given at the same time as chemotherapy or if you already have a heart condition.

If you do develop heart problems, treatment may be stopped temporarily. Occasionally it may need to be stopped permanently. You may need to have treatment for any heart problems that develop as a result of having trastuzumab.

Only a small number of people having trastuzumab develop heart problems and they usually reverse once treatment has finished.

9. Blood clots

People with breast cancer have a higher risk of blood clots. Their risk is higher because of the cancer itself and some treatments for breast cancer.

If the cancer has spread to other parts of the body (secondary breast cancer), this also increases the risk.

Blood clots can be harmful but are treatable so it’s important to report symptoms as soon as possible.

If you experience any of the following symptoms contact your local A&E department, GP or treatment team straight away:

  • pain, redness/discolouration, heat and swelling of the calf, leg or thigh
  • swelling, redness or tenderness where a central line is inserted to give chemotherapy, for example in the arm, chest area or up into the neck
  • shortness of breath
  • tightness in the chest
  • unexplained cough (may cough up blood)

10. Can I get pregnant or breastfeed while having trastuzumab?

Trastuzumab is not usually prescribed during pregnancy and women are advised not to become pregnant as it may be harmful to a developing baby. Some women can still become pregnant even if their periods are irregular or have stopped, so effective barrier contraception such as a condom should be used for at least seven months after treatment finishes.

Breastfeeding is also not recommended while having trastuzumab or within seven months of the last dose.

11. Travel and vaccinations

Depending on whether or not you are having trastuzumab alongside or following chemotherapy, you may or may not be able to have travel or routine vaccinations. If you need a vaccination, discuss this with your treatment team first.



Last reviewed: February 2019
Next planned review begins 2021

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