Trastuzumab deruxtecan (Enhertu)

Trastuzumab deruxtecan is a type of targeted cancer drug. It is also known as Enhertu.

You pronounce trastuzumab deruxtecan as tras-too-zoo-mab deh-rux-tee-can. 

Trastuzumab deruxtecan is a combination of the targeted cancer drug trastuzumab (also known as Herceptin) and a chemotherapy drug called deruxtecan or DXd.

It is a treatment for:

  • HER2 positive Open a glossary item  breast cancer that has spread to other parts of the body (also called advanced, metastatic or secondary breast cancer) and you have already had one or more treatments with a HER2 targeted treatment
  • HER2 positive breast cancer that has spread to other parts of the body and can’t be removed with surgery and you have already had chemotherapy. Or if your cancer came back within 6 months of finishing chemotherapy

How does trastuzumab deruxtecan work?

Some cancers have too much of a protein called human epidermal growth factor receptor 2 (HER2) on the surface of their cells. These are called HER2 positive cancers. HER2 makes the cells grow and divide.

Trastuzumab is a type of targeted drug called a monoclonal antibody. It attaches to the HER2 receptor and can stop the cancer cells from growing. When it attaches to the HER2, it allows the deruxtecan to go into the cancer cell. Inside the cell deruxtecan becomes active and kills the cancer cell.

How do you have trastuzumab deruxtecan?

You have trastuzumab deruxtecan as a drip into your bloodstream.

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.

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

How often do you have trastuzumab deruxtecan?

You have trastuzumab deruxtecan as cycles of treatment. This means that you have the drug and then a rest to allow your body to recover.

Each cycle of treatment lasts 21 days (3 weeks). So, you have the drug once every 3 weeks.

You have the first dose over 90 minutes. If you don’t have a bad reaction to your first treatment, you can usually have all other treatments over 30 minutes.

You continue to have treatment for as long as it helps and the side effects aren't too bad.

Your healthcare team will explain more about how you will have your treatment.


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.

You usually have heart tests such as an echocardiogram (ECHO) or a multigated acquisition (MUGA) scan to build up a picture of how well your heart is working. You usually have one of these before starting treatment and every 3 months during treatment.

What are the side effects of trastuzumab deruxtecan?

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. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. 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, 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

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).

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.

Damage to the lungs

This drug can cause lung problems. They can cause changes to your lung tissue which makes it stiff and leaves scarring. This can make it difficult to breathe.

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


Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 

Bone or muscle pain

You might feel some pain in your bones or muscles. Speak to your doctor or nurse about what painkillers you can take to help with this.

Tiredness and weakness

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.

High temperature (fever)

If you get a high temperature, let your healthcare team know straight away. Ask them if you can take paracetamol to help lower your temperature.

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.

Hair thinning or 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. 

Indigestion or heartburn

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


Contact your advice line if you have diarrhoea, such as if you've had 4 or more loose watery poos (stools) in 24 hours. Or if you can't drink to replace the lost fluid. Or if it carries on for more than 3 days.

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.


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.

Loss of appetite and weight loss

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. 

Heart problems

This drug can weaken the heart muscle, causing changes to how your heart pumps blood around your body. Tell your healthcare team if you develop breathlessness, chest pain, swollen ankles, or changes to your heartbeat.

You have regular heart tests such as an echocardiogram (ECHO) Open a glossary item  to check your heart function. 

Liver changes 

You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.

Skin changes 

You might develop a rash. This could be bumpy or flat or both, itchy, or pus filled.

Less commonly your skin may also become darker or develop lighter patches. 

Low potassium levels

You might develop a low level of potassium in your blood. This can cause muscle cramps, tiredness and heart palpitations. You have regular blood tests to check this.

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:

  • blurred vision
  • dizziness
  • dehydration or feeling thirsty
  • a dry mouth
  • taste changes
  • swollen tummy (abdomen)
  • swollen ankles, feet or face
  • farting (flatulence)
  • kidney changes
  • an allergic reaction which can cause flushing of the skin, shivering, seizures (fits), fever, difficulty breathing, low blood pressure and a fast heartbeat during the infusion or up to 24 hours afterwards
  • inflammation of the stomach lining (gastritis)

What else do you need to know?

Other medicines, foods and drinks

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.

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.

Men having trastuzumab deruxtecan might be able to store sperm before starting treatment. Men having this drug must not freeze or donate sperm during treatment and for at least 4 months after the last dose.

Pregnancy and contraception 

This treatment may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment.

Women must not become pregnant for at least 7 months after the end of treatment. Men should not get someone pregnant for at least 4 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.


Don’t breastfeed during this treatment and for 7 months afterwards. The drug may come through in the 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.


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 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 Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

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