Tucatinib (Tukysa) is a tyrosine kinase inhibitor used to treat metastatic, HER2-postive breast cancer. It is given with another targeted therapy, trastuzumab (Herceptin), and the chemotherapy pill capecitabine (Xeloda) to treat cancers that have grown after previous HER2-targeted treatments.


How tucatinib works

Tucatinib is a small molecule tyrosine kinase inhibitor, or TKI. Certain proteins, called tyrosine kinases, tell breast cancer cells to multiply. Tucatinib blocks these proteins from working to help keep cancer from growing.

Tucatinib molecules are able to pass through the blood-brain barrier a defense in your body that stops many medicines from getting into your brain or central nervous system. Getting through the blood-brain barrier allows tucatinib to treat metastases in the brain more effectively than other treatments.


Who gets tucatinib

Tucatinib is given to people with metastatic, HER2-positive breast cancer that has grown during treatment with a previous targeted therapy — trastuzumab, pertuzumab, ado-trastuzumab emtansine, or a combination of those medicines.


How tucatinib is given

Tucatinib is given as pills that you take twice each day. Capecitabine is also a pill and is taken twice daily for 14 days, followed by a 7 day break. Trastuzumab can be given by vein at an infusion center or as an injection, usually into the thigh. Trastuzumab is given once every 3 weeks.

The makers of tucatinib offer a downloadable treatment tracker to help you manage what treatments you get each day.


Side effects and things to remember

Common side effects experienced with tucatinib include

Tucatinib can also cause serious side effects such as severe diarrhea that may need medical treatment, and liver problems. If you have existing liver problems, you should tell your doctor before starting tucatinib. Your healthcare team will check your blood for any signs of liver problems, but you should report side effects that may be caused by liver problems, such as:

  • itching
  • yellowing of your skin or eyes
  • dark or tea-colored urine
  • pain near your stomach
  • decreased appetite
  • bruising or bleeding that happens more easily than normal
  • tiredness

Tell your doctors about any medicines you are currently taking before starting tucatinib. You should not take tucatinib if you are pregnant or breastfeeding, and you should take steps to avoid getting pregnant or getting your partner pregnant while on tucatinib.


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Reviewed and updated: March 25, 2021

Reviewed by: Tiffany Avery, MD MPH


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