Tucatinib is a type of targeted anticancer drug, which is used in combination with other medications for the treatment of advanced breast cancer. Tucatinib belongs to a class of drugs called tyrosine kinase inhibitors.

Tucatinib targets HER2 (human epidermal growth factor receptor 2) tyrosine kinase. HER2 receptors are involved in the growth and repair of normal breast cells. But, 10 to 20 percent of breast cancers have a faulty HER2 gene, which makes too many copies of itself. This results in HER2 protein overexpression - too many HER2 receptors on the breast cells - which makes the breast cells grow and divided uncontrollably.

Tucatinib works by blocking the activity of HER2, which helps to slow the growth and spread of cancer cells. It is used in combination with trastuzumab and capecitabine because the combination helps patients live longer without their cancer progressing and survive for longer overall.

It was approved by the US Food and Drug Administration (FDA) in 2020.

What is tucatinib used for?

Tucatinib is a prescription medicine used with the medicines trastuzumab and capecitabine to treat adults with:

• human epidermal growth factor receptor-2 (HER2) positive breast cancer that has spread to other parts of the body such as the brain (metastatic), or that cannot be removed by surgery, and
• who have received one or more anti-HER2 breast cancer treatments.

It is not known if tucatinib is safe and effective in children.

Tucatinib is used with the medicines trastuzumab (Herceptin) and capecitabine (Xeloda). Also read the patient information that may come with these medicines.

What should I tell my doctor before taking tucatinib?

Before taking tucatinib, tell your healthcare provider about all of your medical conditions, including if you have liver problems.

• Take tucatinib exactly as your healthcare provider tells you.
• Tucatinib is used with the medicines trastuzumab and capecitabine. Your healthcare provider will tell you the dose of trastuzumab and capecitabine you will take and how you will receive them.
• Take tucatinib 2 times a day, with or without a meal.
• Take tucatinib about 12 hours apart or at the same times every day.
• Swallow tucatinib tablets whole. Do not chew, crush, or split tucatinib tablets before swallowing. Do not take tucatinib tablets if they are broken, cracked, or damaged.

The recommended dosage of tucatinib is 300 mg taken orally twice daily with or without food. For patients with severe hepatic impairment, the recommended dosage is 200 mg orally twice daily.

See full prescribing information for additional information about tucatinib dosing.

Before taking tucatinib, tell your healthcare provider about all of your medical conditions, including if you have liver problems.

If you vomit or miss a dose of tucatinib, take your next dose at your regular time.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture not in the bathroom. Do not remove the desiccant (drying agent) from the bottle. Properly dispose of any unused tablets 3 months after opening the bottle.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Unless your doctor tells you otherwise, continue your normal diet.

Tucatinib may cause serious side effects, including:

• Diarrhea. Diarrhea is common with tucatinib and can sometimes be severe. Tell your healthcare provider if you have a change in your bowel movements or severe diarrhea. Severe diarrhea can lead to loss of too much body fluids (dehydration), low blood pressure, kidney problems and death. Your healthcare provider may prescribe medicines to treat your diarrhea during treatment with tucatinib.
• Liver Problems. Tucatinib can cause severe liver problems. Your healthcare provider will do blood tests to check your liver function before and every 3 weeks during treatment with tucatinib, or as needed. Tell your healthcare provider right away if you have any signs and symptoms of liver problems including:
  • itching
  • yellowing of your skin or eyes
  • dark or brown urine (tea-colored)
  • pain in the upper right side of your stomach-area (abdomen)
  • feel very tired
  • decreased appetite
  • bleeding or bruising more easily than normal

The most common side effects of tucatinib:

• diarrhea
• rash, redness, pain, swelling or blisters on the palms of your hands or soles of your feet
• nausea
• tiredness
• increased liver function blood tests
• vomiting
• mouth sores (stomatitis)
• decreased appetite
• stomach-area (abdomen) pain
• headache
• low red blood cell counts (anemia)
• rash

Your healthcare provider may change your dose of tucatinib, temporarily stop, or permanently stop treatment with tucatinib if you have certain side effects.

Tucatinib may cause fertility problems in males and females, which may affect the ability to have children. Talk to your healthcare provider if you have concerns about fertility.

These are not all of the possible side effects of tucatinib. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Tucatinib may affect the way your other medicines work, and other medicines may affect the way tucatinib works.

Know the medicines you take. Keep a list of all the medicines you take and show it to your healthcare provider and pharmacist every time you get a new medicine.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests before and during your treatment to check your body's response to tucatinib. Your doctor may order a lab test before you begin your treatment to see whether your cancer can be treated with tucatinib.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.