Trastuzumab emtansine (Kadcyla)

Trastuzumab emtansine is a type of targeted cancer drug. It is also known as Kadcyla. 

You pronounce it as tras-too-zoo-mab em-tan-seen.

Trastuzumab emtansine is a combination of the drug trastuzumab (also known as Herceptin) and a chemotherapy drug called emtansine. 

It is a treatment for HER2 positive Open a glossary item breast cancer. You might be offered it if you have: 

  • early HER2 positive breast cancer and there is still some cancer in the breast or lymph nodes after having surgery, taxane chemotherapy and trastuzumab or pertuzumab
  • HER2 positive breast cancer that has spread or come back (advanced) after previous treatment with chemotherapy or trastuzumab

How does trastuzumab emtansine work?

Some breast 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 cancer drug called a monoclonal antibody. Trastuzumab attaches to the HER2 receptor. When it attaches to the HER2, it allows the emtansine to go into the cancer cell. Inside the cell emtansine becomes active and kills the cancer cell.

How do you have trastuzumab emtansine?

You have trastuzumab emtansine as a drip into your bloodstream (intravenously).

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

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 often do you have trastuzumab emtansine?

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

You have trastuzumab emtansine every 3 weeks.

You have the first treatment over 90 minutes. You usually have your first treatment as an inpatient to monitor you for any reactions to the drug. If the first one went well you might have the next treatments over 30 minutes. 

If you're having trastuzumab emtansine after surgery for early breast cancer you might have up to 14 cycles.

For breast cancer that has come back or spread around the body, you continue to have treatment for as long as it helps and the side effects aren't too bad.

If you're having radiotherapy as well as trastuzumab emtansine your treatment is usually spaced to reduce the risk of having radiation related side effects. Your healthcare team will go through this with you. 


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 if working. You usually have one of these before starting treatment and every 3 months during treatment. 

What are the side effects of trastuzumab emtansine?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

This treatment affects the immune system. This may cause inflammation in different parts of the body which can cause serious side effects. They could happen during treatment, or some months after treatment has finished. In some people, these side effects could be life threatening.

When to contact your team

Your doctor, pharmacist or nurse will go through the possible side effects. They will monitor you closely 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 healthcare team 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:

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.

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 (known as petechiae).

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. 

Breathlessness and looking pale

You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

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.


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.


Constipation Open a glossary item 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 healthcare team if you think you are constipated. They can prescribe a laxative.

Dry mouth

A dry mouth is also called xerostomia (pronounced zero-stow-mee-a). Talk to your healthcare team if you have this. They can give you artificial saliva to help with a dry mouth. It can also help to drink plenty of fluids.

Urinary tract infections (UTIs)

Tell your doctor or nurse if you think you might have a urinary tract infection. You might find it difficult to pass urine, want to go with some urgency or are going more often. There may be pain or burning when you go. You may see blood in your urine, or your urine might smell bad or look cloudy.

Difficulty sleeping

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. 


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

Tummy (abdominal) cramps

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

Cough and difficulty breathing

It is important to tell your doctor or nurse if you have a cough. This could be due to an infection, such as pneumonia. Or it could be caused by changes to the lung tissue, making it less flexible.

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.

Joint or muscle pain

You might feel some pain from your muscles and joints. 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.

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:

  • increased risk of getting an infection due to a drop in the levels of white blood cells - symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell

  • 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 after

  • heart problems which can include shortness of breath, swollen arms or ankles, chest pain and changes to heartbeat

  • low levels of potassium in blood

  • feeling dizzy

  • changes to taste

  • problems with your memory

  • eye problems such as dry eyes, watery eyes, blurred vision, redness of the eye or an infection

  • high blood pressure

  • indigestion which can cause bloating, feeling sick, discomfort and burping

  • swelling in the arms and legs due to a build up of fluid

  • feeling shivery (chills)

  • thinning of your hair

  • skin problems such as a rash, itchy skin and hives

  • nail changes

  • the palms of your hands and soles of your feet might become sore and red and the skin might peel - this is known as palmar-plantar syndrome and can cause tingling, numbness, pain and dryness

Rare side effects

This side effects happens in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:

  • breathing problems due to inflammation of the lungs (pneumonitis) - let your doctor or nurse know straight away if you suddenly become breathless or develop a cough

  • severe liver problems which can cause your skin and the whites of your eyes to go yellow (jaundice). You may also have bloating, swelling of your tummy (abdomen) and bleeding

  • inflammation around the drip site which can cause redness, pain, swelling or leaking. Let your healthcare team know straight away if this happens

Coping with side effects

We have more information about side effects and tips on how to cope with them.

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.

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Loss of fertility

It is not known whether this treatment affects fertility Open a glossary item in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Contraception and pregnancy

This treatment might harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you're having treatment and for a few 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.

You should continue to take your contraception for at least 7 months after your last dose of trastuzumab emtansine. Talk to your doctor before stopping your contraception.


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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