Tucatinib (Tukysa)

Tucatinib is a targeted therapy. Targeted therapy is the name given to a group of drugs that block the growth and spread of cancer. They target and interfere with processes in the cells that help cancer grow.  

Tucatinib belongs to a group of cancer drugs called tyrosine kinase inhibitors (TKIs).

Tucatinib is the drug’s non-branded name. Its brand name is Tukysa.

Tucatinib can be used to treat breast cancer that has spread to another part of the body (metastatic breast cancer) or that cannot be removed by surgery.

You may tucatinib if:

• Your breast cancer is HER2-positive
• And you have already had 2 or more other treatments specifically for HER2-positive breast cancer

Some breast cancer cells have a higher-than-normal level of a protein called HER2 on their surface, which makes them grow more quickly. 

This is known as HER2-positive breast cancer. 

Tucatinib blocks the HER2 protein in the cancer cells, which stops the cells from growing and spreading.

The blood–brain barrier is a natural filter that protects the brain from harmful chemicals. It only allows certain substances to pass from the blood to the brain tissues. Tucatinib can cross the blood–brain barrier, so it can help treat HER2-positive breast cancer that has spread to the brain. 

You take tucatinib as a tablet twice a day, every day. You can take it with or without food.

You’ll have tucatinib together with trastuzumab (Herceptin) and capecitabine.

On the days you take capecitabine, you can take it at the same time as tucatinib.

What if I miss a dose?

If you miss a dose of tucatinib or you’re sick (vomit) soon after taking it, do not take an extra dose to make up for the one you missed. 

Take the next dose at the usual time and speak to someone in your treatment team.

How long will I take tucatinib for?

You’ll have tucatinib for as long as your treatment team feels you’re benefitting from the drug and any side effects are manageable.

Blood tests while taking tucatinib

While you’re taking tucatinib you’ll have regular blood tests to check the levels of your blood cells and how well your liver and kidneys are working.

Like any treatment, tucatinib 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. 

As you have tucatinib with trastuzumab and capecitabine, it’s sometimes difficult to know which side effects are being caused by which treatment.

If you’re worried about any side effects, regardless of whether they’re listed here, talk to your treatment team. 

Common side effects

Common side effects happen to more than 10 in every 100 people who take the drug.

Effects on the blood

Tucatinib, when taken together with trastuzumab (Herceptin) and capecitabine, can temporarily affect the number of blood cells in the body. Blood is made up of red cells, white cells and platelets. 

You’ll have regular blood tests. If these show the number of blood cells is too low, your treatment may be delayed or the dose changed. 

Risk of infection 

Not having enough white blood cells can increase your risk of getting an infection. 

Before starting treatment you should be given a 24-hour contact number or told who to contact if you feel unwell at any time during your treatment, including overnight or at the weekends.

You may need treatment if you get an infection.

Sometimes your treatment team may recommend injections of drugs called growth factors. This helps the body make more white blood cells to reduce your risk of infection.  

Anaemia

Having too few red blood cells is called anaemia. If you feel breathless, dizzy or particularly tired, let your treatment team know.

Bruising and bleeding 

Tucatinib, when taken together with trastuzumab (Herceptin) and capecitabine, can reduce the number of platelets.

Platelets help the blood to clot.

If your platelets are low, you may: 

• Bruise more easily 
• Have nosebleeds 
• Notice that your gums bleed when you brush your teeth 
• Take longer to stop bleeding if you cut yourself 

Tell your treatment team if you have any of these symptoms. 

Diarrhoea

Contact your chemotherapy team if you have diarrhoea 3 or more times in 24 hours, compared to what’s usual for you.

Skin reactions

You may develop a rash anywhere on your body or your skin might look a different colour to usual. This could be red, darker than your usual skin tone and itchy. You may feel flushed. Your treatment team might prescribe medicine to help. 

If you have skin reactions, tell your treatment team so they can monitor your symptoms.

Some people have a skin reaction called hand-foot syndrome, also called palmar-plantar syndrome.

It usually affects the palms of the hands and soles of the feet. You may also have symptoms in other areas, such as the skin on the knees or elbows.

Nausea and vomiting 

You may feel sick (nausea) and be sick (vomit).

You’ll be prescribed anti-sickness drugs to reduce nausea or stop it happening.

If you continue to feel sick or be sick, tell your treatment team as they may be able to change your anti-sickness drugs.

Try to eat small meals throughout the day and drink often.

Extreme tiredness (cancer-related fatigue)

Fatigue is extreme tiredness that does not go away with rest or sleep. It’s one of the most common symptoms in people with metastatic breast cancer. 

Fatigue has many causes, from the emotional impact of a diagnosis to side effects of treatment or growth and spread of the cancer. 

If you think you have fatigue, tell your GP or treatment team. They can assess you and offer advice on how to manage your energy levels. 

Find out more about managing fatigue. 

Sore mouth 

Looking after your mouth, including your teeth and gums, is very important during treatment.

You may be given mouthwash to try to reduce soreness and prevent mouth ulcers developing. It’s a good idea to use a small, soft toothbrush during this time.

See your dentist for a check-up before treatment begins and avoid dental work during these treatments if possible.

If you do need to have dental work during treatment, talk with your treatment team about the best time to have this. 

If you’re having difficulty registering with a dentist, let your treatment team know.

Loss of appetite

You may not feel like eating, especially if you’re feeling sick. Your sense of taste may also change, and some food and drink may taste different. 

Eating small, frequent meals or snacks can help keep up your food intake. If you struggle to maintain a healthy weight, ask your GP or treatment team about being referred to a dietitian.

Liver problems

Tucatinib can affect how the liver works. 

You’ll have blood tests to check how your liver is working while you’re having treatment.

Treatment may need to be delayed or the dose changed if the blood tests show any problems with your liver.

If you have any of the following symptoms, contact your treatment team straight away:

• Yellowing of your skin or the whites of your eyes (jaundice)
• Pain on your right side under the ribs
• Bleeding or bruising more easily than normal
• Feeling more tired
• Itching
• Your pee being dark brown

Other common side effects

Other common side effects of tucatinib include:

• Joint pain
• Weight loss
• Nosebleeds
• Numbness and tingling in hands or feet (peripheral neuropathy)

Your treatment team can advise you on how to manage these

Seizures (fits)

People having tucatinib for metastatic breast cancer in the brain may have seizures.

Seizures can affect people in different ways. Some seizures cause loss of consciousness and the body may jerk and twitch. Others happen without much movement, causing problems like loss of awareness, unusual sensations or not being able to talk.

Seizures typically pass in a few seconds or minutes. They can happen without warning and can be frightening for you and people around you.

It’s important that you contact your 24-hour advice line number or go straight to A&E if you have a seizure.

Allergic reaction

If you have an allergic reaction to tucatinib, it’s more likely to happen the first time you have the treatment.

Contact your hospital immediately if you notice any of the following symptoms: 

• Itchy red or discoloured bumps on your skin (these may be harder to see on black or brown skin) 
• Swelling in your lips, tongue or throat 
• Breathlessness, wheezing, a bad cough or sudden difficulty breathing 
• Tight chest or chest pain 

If you have a severe reaction, treatment will be stopped immediately. If you have a less severe reaction, you may need to take medication before future treatments to reduce the risk of further reactions. 

Blood clots

People with breast cancer have a higher risk of blood clots such as a DVT (deep vein thrombosis). 

If you have a DVT, there’s a risk part of the blood clot could break away and travel to the lung. This is known as a pulmonary embolism (PE).

Blood clots can be life-threatening and should be treated quickly. 

Medicines to avoid when taking tucatinib

There are several drugs that you should not take with tucatinib, including some antibiotics, heart and epilepsy medication. Tell your treatment team about any prescribed or over-the-counter medicines you’re taking.

Many people consider taking herbal medicines or supplements while having treatment for breast cancer.

You should not take anything containing St John’s wort while you’re taking tucatinib. Ask your treatment team before taking any herbal medicines or supplements.

Sex, contraception and pregnancy

You can still have sex during treatment. It’s thought some drugs used to treat breast cancer cannot pass into vaginal fluids or semen, but this cannot be completely ruled out. 

Most treatment teams will advise using barrier methods of contraception, such as condoms or female condoms, during treatment and for 7 days after your last treatment. 

You’re advised not to become pregnant while having treatment because tucatinib can harm a developing baby. If you have not been through the menopause, talk to your team about the most suitable method of contraception for you. It’s still possible to become pregnant even if your periods are irregular or have stopped naturally or because of treatment for breast cancer.

Fertility

It’s not known if tucatinib affects your ability to get pregnant (fertility).

Conversations about fertility can be hard. It’s important to discuss any fertility concerns with your treatment team before you begin your treatment. 

If you were diagnosed with locally advanced or metastatic breast cancer before you started or completed a family, you may be concerned about your fertility.

You can talk to your treatment team about fertility preservation options.

Breastfeeding

Breastfeeding is not recommended while having tucatinib, or within 1 week of the last dose. This is because there’s a risk the drugs could be passed on through breast milk.

Travel and vaccinations

If you’re planning a holiday or need to travel overseas, check with your treatment team first. 

You should not have any live vaccines while you’re having treatment.

For more information about vaccines, including COVID-19 and flu vaccines, see our information on vaccines and breast cancer.

If you’ve been diagnosed with metastatic breast cancer, you might be feeling lonely or isolated. Many people experience this and support is available.

Your treatment team can help with any questions you have. And you can call our helpline for information and support. See the bottom of this page for ways to get in touch.

You might find it helps to talk to someone who has been through a similar experience to you. You can join one of our chat groups or visit our online forum.

And our Living with Secondary Breast Cancer services are also here for you. Choose the type of support that suits you and you’ll be able to talk, listen and learn with people who understand the challenges that metastatic breast cancer can bring.