Trastuzumab emtansine (Kadcyla) | Cancer Research UK
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What trastuzumab emtansine is

Trastuzumab emtansine is pronounced trast-oo-zoo-mab em-tan-seen. It is a combination of a drug called trastuzumab and a drug called emtansine. It used to be called T-DM1. Trastuzumab is a type of biological therapy called a monoclonal antibody. Emtansine is a chemotherapy drug that can kill cancer cells.

Trastuzumab emtansine also has the brand name Kadcyla (pronounced cad-sigh-lah]. It is a treatment for HER2 positive breast cancer that has spread or come back after previous treatment. You normally only have it if you have previously had trastuzumab (Herceptin) treatment.

You may also have trastuzumab emtansine as part of clinical trials for other types of cancer.


How trastuzumab emtansine works

Some breast cancers have too much of a protein called human epidermal growth factor receptor 2 (HER2 protein), on the surface of their cells. These are called HER2 positive cancers. The HER2 makes the cancer cells grow and divide. Trastuzumab attaches to the receptor. When trastuzumab attaches to the receptor it allows the emtansine to go into the cancer cell. The emtansine then becomes active and kills the cancer cell. 

Before prescribing trastuzumab emtansine your doctor will check a sample of your tumour for the HER2 protein.


How you have trastuzumab emtansine

Trastuzumab emtansine is a clear liquid. You have it through a drip into a vein (intravenously). You can have it through a thin, short tube (a cannula) put into a vein in your arm each time you have treatment. Or you may have it through a central line), a portacath), or a PICC line). These are long, plastic tubes that give the drugs directly into a large vein in your chest.

You have the treatment every 3 weeks. You have the first treatment over 90 minutes. If this goes well you can have the next treatments over 30 minutes.

You usually continue having the treatment for as long as it controls the cancer. But if the side effects get too bad your doctor will stop the treatment.

We've listed the side effects associated with trastuzumab emtansine below. The side effects may be different if you are having it with other drugs.

You can use the links to find out more about each side effect. Where there is no link, please go to our cancer drug side effects section or use the search box at the top of the page.


Common side effects

More than 10 in 100 people have one or more of these side effects

  • Tiredness, weakness and breathlessness from a drop in red blood cells (anaemia) occurs in more than 6 out of 10 people (62%). You may need a blood transfusion
  • Bruising more easily from a drop in platelets affects more than 3 out of 10 people (31%). You may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)
  • Liver changes occur in almost 3 out of 10 people (28%). The changes are very mild and unlikely to cause symptoms. They will almost certainly go back to normal when treatment is finished. You will have regular blood tests to check how well your liver is working
  • Low levels of potassium in your blood happen in more than 3 out of 10 people (34%). You may not have any symptoms from this but your doctor or nurse will do regular blood tests to check the levels
  • Muscle or joint pain affects a quarter of people (25%)
  • Headaches happen in a quarter of people (25%)
  • Numbness or tingling in fingers and toes can cause difficulty with fiddly things such as doing up buttons. This starts within a few days or weeks and usually goes within a few months of finishing treatment. You may also have itching or a crawling sensation on the skin
  • Feeling or being sick is usually well controlled with anti sickness medicines
  • Diarrhoea – drink plenty of water and tell your doctor or nurse if you are worried about how bad it is. Let your nurse know if it continues for more than 3 days
  • Difficulty sleeping
  • A dry mouth
  • Bladder infections leading to a need to pass urine often and pain or soreness when passing urine. Let your doctor or nurse know as soon as possible if you have this. They can give you medicines to help
  • Constipation – your doctor or nurse may give you medicines to help prevent this. Tell them if you are constipated for more than 3 days
  • Stomach ache
  • A sore mouth
  • Flu like symptoms – you may have fever, chills and muscle aches but taking paracetamol can help
  • Skin rashes or your skin may be dry and itchy
  • Women may stop having periods but this may be temporary
  • Loss of fertility – you may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future. Men may be able to store sperm before starting treatment

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these side effects

  • A reaction while the drug is given happens in around 4 out of 100 people (4%). This causes chills, fever, swelling of the face and lips, and possibly an itchy rash, feeling sick, breathlessness, wheezing, a headache, flushes, dizziness and faintness. If you have a reaction your nurse will slow the drip for a while
  • An increased risk of getting an infection from a drop in white blood cells. You may have headaches, aching muscles, a cough, a sore throat, pain passing urine, or you may feel cold and shivery. If you have a severe infection this can be life threatening. Contact your treatment centre straight away if you have any of these effects or if your temperature goes above 38°C
  • Dry eyes, watery eyes or blurred vision – don’t drive or operate machinery if you have blurred vision
  • Red eyes or an eye infection
  • Higher amounts of bilirubin in your blood – during treatment you will have regular blood tests to check your bilirubin levels
  • Indigestion
  • Fluid build up in your arms or legs causing swelling
  • Raised blood pressure
  • Dizziness
  • Taste changes
  • Difficulty remembering things
  • Hair thinning or hair loss
  • Some people develop soreness, redness and peeling on the palms of the hands and soles of the feet (palmar–plantar syndrome). This may cause tingling, numbness, pain and dryness
  • Nail changes
  • Heart problems affect about 2 out of 100 people (2%). Let your doctor or nurse know if you have breathlessness when resting or lying flat, chest pain, swollen ankles or arms, or a sensation of your heart beating (palpitations)

Rare side effects

Fewer than 1 in 100 people have these side effects.

  • Changes in lung tissue may lead to a cough or breathlessness. Let your doctor or nurse know if you are breathless or have a dry cough. You may need to stop having the treatment
  • Yellowing of the skin and whites of the eyes (jaundice) due to liver cells releasing substances into the blood. Let your doctor or nurse know straight away if you have this. Your doctor may need to stop the treatment
  • A bloated tummy (abdomen) – let your doctor or nurse know straight away if you have this
  • Inflammation around the drip site – if you notice any signs of redness, pain, swelling or leaking at your drip site, tell your chemotherapy nurse straight away

Important points to remember

You may get a few of the side effects mentioned on this page. A side effect may get worse through your course of treatment. Or you may have more side effects as the course goes on. This depends on

  • How many times you've had a drug before
  • Your general health
  • How much of the drug you have (the dose)

Coping with side effects

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Other medicines

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 6 months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


Breastfeeding is not advisable during this treatment and for 6 months afterwards. The drug may come through in the breast milk.



You should not have immunisations with live vaccines while you are having this treatment or for at least 6 months afterwards. In the UK, these include rubella, mumps, measles (usually given together as MMR), BCG, yellow fever and Zostavax (shingles vaccine).

You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered from your treatment. It is safe to have the flu vaccine.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with vaccines you take by mouth (oral vaccines), but not many people in the UK have these now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.


More information about trastuzumab emtansine treatment

We don’t list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at

If you have a side effect we don’t mention here and you think may be due to this treatment, you can report it to the Medicines Health and Regulatory Authority (MHRA) at

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Updated: 16 April 2014