Trastuzumab emtansine (Kadcyla)

1. What is trastuzumab emtansine?
2. Who might be offered trastuzumab emtansine?
3. How does trastuzumab emtansine work?
4. How is trastuzumab emtansine given?
5. Common side effects of trastuzumab emtansine
6. Less common side effects of trastuzumab emtansine
7. Rare side effects of trastuzumab emtansine
8. Blood clots
9. Sex and contraception
10. Travel and vaccinations

1. What is trastuzumab emtansine?

Trastuzumab emtansine is a targeted (biological) therapy. Its generic (non-branded name) is trastuzumab emtansine. Its brand name is Kadcyla.

Trastuzumab emtansine is a combination of two drugs:

  • trastuzumab (Herceptin), which belongs to a group of drugs called targeted (biological) therapies. Targeted therapies block the growth and spread of cancer. They target and interfere with processes in the cells that help cancer grow
  • emtansine, which is a chemotherapy drug

2. Who might be offered trastuzumab emtansine?

You may be offered trastuzumab emtansine if you have HER2 positive secondary breast cancer or a regional recurrence (where surgery is not possible), and have already had trastuzumab and chemotherapy drugs called taxanes, either together or separately.

Trastuzumab emtansine is widely available across the UK.

3. How does trastuzumab emtansine work?

Some breast cancer cells have a higher than normal level of a protein called HER2 on their surface (called HER2 positive breast cancer). This stimulates them to grow.

There are various tests to measure HER2 levels which are done on breast tissue removed during a biopsy or surgery. If your cancer is found to be HER2 negative, then trastuzumab emtansine will not help you.

Trastuzumab attaches to the HER2 proteins (also called receptors) and can stop them growing. It also helps the body’s immune system to destroy cancer cells.

When the trastuzumab attaches to the receptors, it delivers emtansine directly into the breast cancer cells. The emtansine can destroy the cancer cells but leave normal cells relatively unharmed which means there are usually fewer side effects.

4. How is trastuzumab emtansine given?

Trastuzumab emtansine is given through a drip (infusion) into a vein (intravenously). You will have the first infusion over 90 minutes. You’ll then be monitored for at least a further 90 minutes to make sure you don’t have a bad reaction to the treatment.

If you don’t have a bad reaction to your first infusion, further infusions can usually be given over 30 minutes and monitored for at least a further 30 minutes.

You’ll have trastuzumab emtansine as an outpatient every three weeks for as long as your specialist team feels you’re benefiting from the drug and you don’t have any problems with it.

5. Common side effects of trastuzumab emtansine

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

If you’re concerned about any side effects, regardless of whether they’re listed here, talk to your cancer specialist (oncologist).

Effects on the blood

Trastuzumab emtansine can temporarily affect the number of healthy blood cells in the body. Blood cells (white blood cells, red blood cells and platelets) are released by the bone marrow (the spongy material found in the hollow part of bones) to replace those which are naturally used up in the body. Trastuzumab emtansine reduces the ability of the bone marrow to make these cells.

You’ll have regular blood tests to check your blood count. If the number of blood cells is too low, your next trastuzumab emtansine treatment may be delayed or the dose reduced.

Bruising and bleeding

Trastuzumab emtansine can reduce the number of platelets (which help the blood to clot). You may bruise more easily, have nosebleeds or your gums may bleed when you brush your teeth. Tell your specialist team if you notice any of these symptoms.


Having too few red blood cells is called anaemia. If you feel particularly tired, breathless or dizzy, let your specialist team know. A blood transfusion may be necessary during your treatment if the number of red blood cells falls significantly.

Risk of infection

Not having enough white blood cells can increase the risk of getting an infection. You may need to be treated with antibiotics or other drugs that help produce more white blood cells.

Contact your hospital immediately if:

  • you have a high temperature (over 37.5°C) or low temperature (under 36°C), or whatever your chemotherapy team has advised
  • you suddenly feel unwell, even with a normal temperature
  • you have any symptoms of an infection, for example a sore throat, a cough, a need to pass urine frequently or feeling cold and/or shivery

Fatigue (extreme tiredness)

It’s common to feel extremely tired during your treatment. There are different ways of coping with and managing fatigue. You can speak to your specialist team or contact Breast Cancer Care for more information and support.

Muscle and/or joint pain

Let your specialist team know if you have muscle or joint pain. They can prescribe pain relief to help with this.


Trastuzumab emtansine may cause headaches. Ask your specialist team about taking pain relief.

Sore mouth and taste change

Your mouth may become sore or dry and you may get ulcers. You may be given mouthwash to reduce soreness of the mouth and gums and to try to stop mouth ulcers developing. Good mouth hygiene is very important during treatment. It’s advisable to see your dentist for a dental check-up before your treatment begins. Check with your specialist before having any dental work done.

Your taste can change and some food may taste different (for example more salty, bitter or metallic). It can be helpful to experiment with different types of food to find the ones you can eat.

Shortness of breath and coughing

Trastuzumab emtansine can cause changes to the lungs. Let your specialist team know if you start to feel breathless or develop a cough.

Numbness and tingling in hands or feet

Some people experience numbness or tingling in their hands and feet, known as peripheral neuropathy. This is due to the effect of the drug on the nerves. If you have numbness or tingling, mention this to your specialist so that the symptoms can be monitored.

Difficulty sleeping

For some people, trastuzumab emtansine can affect sleep. If you have difficulty sleeping (insomnia) you may benefit from simple, practical measures such as limiting caffeine, keeping your room dark and quiet and going to bed and getting up at the same time each day. Relaxation exercises can also be helpful. There are CDs, podcasts and phone apps that can guide you through these techniques. If your insomnia is persistent, your GP may prescribe something to help you sleep.

Low levels of potassium in the blood

You will have regular blood tests before and during treatment to check your potassium levels. If your potassium levels are low your specialist may prescribe supplements. Potassium levels usually go back to normal when your treatment finishes.

6. Less common side effects of trastuzumab emtansine

Allergic reaction

If you have an allergic reaction to trastuzumab emtansine, it’s more likely to happen the first time you have the treatment. This is why your first treatment is given over 90 minutes. Before your treatment starts, you’ll be given drugs to reduce the risk of an allergic reaction.

You’ll be monitored closely during your treatment so that any reaction can be dealt with immediately. Symptoms include flushing, skin rash, itchiness, back pain, shortness of breath, faintness, fever or chills.

Nausea and vomiting

You may experience nausea (feeling sick) and vomiting (being sick), but most people will not actually be sick. You’ll be prescribed anti-sickness drugs to take home to reduce nausea or stop it happening. If you continue to feel sick or vomit, tell your chemotherapy nurse or cancer specialist as they may be able to change your anti-sickness drugs.

Diarrhoea or constipation

You may have diarrhoea or constipation but your specialist team or GP can prescribe medicine to help control it. Contact your specialist team if you have four or more episodes of diarrhoea within a 24-hour period.

Heart changes

Trastuzumab emtansine may cause heart changes by weakening the heart muscle. This is usually temporary, but for a small number of people it may be permanent. Before you start treatment your specialist will arrange a heart (cardiac) function test to make sure your heart is working normally. This could be an echocardiogram (echo) or a multiple-gated acquisition.

Contact your specialist team if you develop any breathlessness, chest pain, changes to your heartbeat or swollen ankles.

Skin changes

You may get a rash and your skin may be itchy. Let your specialist team know if you have any skin changes as they can prescribe creams or tablets to help.

Hand-foot (palmar plantar) syndrome

The palms of the hands and the soles of the feet can become red and sore. Sometimes you may also notice a tingling sensation, numbness or some swelling.

Your skin may also become red, dry and flaky. This should improve if the treatment is delayed or if the dose is reduced. Using a glycerine-based moisturising cream can also help.

If you experience skin reactions, mention this to your specialist team so that the symptoms can be managed.

Hair thinning

You may notice your hair thins while having your treatment. However, it is unusual to lose your hair.

7. Rare side effects of trastuzumab emtansine

Liver changes

Trastuzumab emtansine can affect how the liver works. You will have blood tests to check your liver function while you’re having treatment.

Sometimes treatment may need to be delayed or the dose reduced if the blood tests show any problems with your liver.

Dizziness and memory problems

Tratuzumab emtansine can cause you to feel dizzy or to become forgetful. Let your specialist team know if you experience these symptoms.

8. 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. Having trastuzumab emtansine increases the risk of blood clots such as a deep vein thrombosis (DVT). People with a DVT are at risk of developing a pulmonary embolism. This is when part of the blood clot breaks away and travels to the lung.

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 specialist 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)

Find out more about blood clots.

9. Sex and contraception

You’re advised not to become pregnant while you’re having treatment because trastuzumab emtansine may have a harmful effect on a developing baby. If you haven’t been through the menopause, talk to your team about the most suitable method of contraception for you. You should continue using contraception for at least seven months after your last dose of trastuzumab emtansine.

You can still have sex during treatment. It’s not known if chemotherapy can pass into vaginal fluids or semen. Most hospital specialists will advise using barrier methods of contraception, such as condoms.

10. Travel and vaccinations

Travel vaccinations

Vaccines may be less effective if given during treatment. You shouldn’t have any live vaccines (vaccines containing active viruses) while having chemotherapy as they could be harmful and cause infections. Live vaccines include those that protect against measles, rubella, yellow fever and typhoid.

If you’re planning a trip and need vaccinations, discuss this with your specialist team.

Flu vaccination

Anyone with a reduced immunity to infection should have a flu vaccine. This includes people having or due to have chemotherapy. The flu vaccine is not a live vaccine.

If you’re already having chemotherapy, talk to your chemotherapy specialist or breast care nurse about the best time to have your flu jab.

Last reviewed: August 2017
Next planned review begins 2019

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