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What's the mechanism of action for tucatinib?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Jan 25, 2023.

Official answer


Tucatinib (Tukysa) is a human epidermal growth factor receptor-2 (HER2) inhibitor that works by blocking the HER2 protein to help slow or stop cancer cell growth in patients with advanced breast cancer or colorectal cancer. Some cancers have an over-expression of the HER2 protein causing increased growth and spread of cancer cells.

Tucatinib, an oral targeted drug therapy, is very selective for the HER2 protein and works inside the cell. Tucatinib binds to tyrosine kinase (an enzyme) of HER2, reducing PI3-kinase and MAP-kinase signaling. Reduced signaling helps to block cell growth and leads to cell death. Tucatinib is classified as a HER2 tyrosine kinase inhibitor.

Related information: List of HER2 Inhibitors

How is tucatinib used?

  • Tucatinib (Tukysa) is used with the medicines trastuzumab (Herceptin) and capecitabine (Xeloda) in adult patients with HER2-positive breast cancer, including cancer that has spread to the brain. It is given to patients who have already received one or more anti-HER2 breast cancer treatments, but are no longer effective.
  • It is also used in combination with trastuzumab to treat adult patients with RAS wild-type HER2-positive unresectable or metastatic colorectal cancer that has progressed following treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy.
  • It is used when the cancer has spread in the body (metastatic) or cannot be removed with surgery (unresectable).

The FDA approved Tukysa for colorectal cancer under an "accelerated approval". This means that continued approval for this use may depend upon results of further clinical studies looking at its effectiveness in colorectal cancer.

This is not all the information you need to know about Tukysa (tucatinib) for safe and effective use and does not take the place of talking to your doctor about your treatment. Review the full product information here, and discuss this information and any questions you have with your doctor or other health care provider.

  • Tukysa (tucatinib) product information. Seagen. Bothell, WA. Revised 1/2023. Accessed Jan 25, 2023 at
  • Mechanism of Action. Seagen Inc. Accessed April 22, 2021 at

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