Tukysa (chemical name: tucatinib) in combination with Herceptin (chemical name: trastuzumab) and Xeloda (chemical name: capecitabine) is approved by the U.S. Food and Drug Administration to treat metastatic HER2-positive breast cancer or locally advanced HER2-positive breast cancer that can’t be completely removed with surgery, after the cancer has been treated with at least one anti-HER2 medicine.
Locally advanced breast cancer is breast cancer that has spread to tissue near the breast, but not to parts of the body away from the breast. Metastatic breast cancer is breast cancer that has spread to parts of the body away from the breast, such as the bones or liver.
Doctors call cancer that can’t be completely removed with surgery “unresectable.”
Tukysa is a pill taken by mouth.
How Tukysa works
Tukysa is a tyrosine kinase inhibitor. Tyrosine kinases are enzymes that help control how cells grow and divide, among other functions. If the enzyme is too active or if a cell has too much of the enzyme, it can make cells grow uncontrollably. Tukysa blocks a specific area of the HER2 gene in cancer cells, which stops the cells from growing and spreading.
Is Tukysa right for you?
Tukysa can be used to treat metastatic HER2-positive breast cancer that has previously been treated with at least one anti-HER2 medicine.
Tukysa also can be used to treat locally advanced HER2-positive breast cancer that can’t be removed with surgery and also has previously been treated with at least one anti-HER2 medicine.
There are several tests used to find out if breast cancer is HER2-positive. If you have been previously treated with an anti-HER2 therapy, one or more of these tests was used to figure out if the cancer was likely to respond. Two of the most common tests are:
The IHC test uses a chemical dye to stain the HER2 proteins. The IHC gives a score of 0 to 3+ that measures the amount of HER2 proteins on the surface of cells in a breast cancer tissue sample. If the score is 0 to 1+, it’s considered HER2-negative. If the score is 2+, it's considered borderline. A score of 3+ is considered HER2-positive.
If the IHC test results are borderline, it’s likely that a FISH test will be done on a sample of the cancer tissue to determine if the cancer is HER2-positive.
The FISH test uses special labels that are attached to the HER2 proteins. The special labels have chemicals added to them so they change color and glow in the dark when they attach to the HER2 proteins. This test is the most accurate, but it is more expensive and takes longer to return results. This is why an IHC test is usually the first test done to see if a cancer is HER2-positive. With the FISH test, you get a score of either positive or negative (some hospitals call a negative test result “zero”).
What to expect when taking Tukysa
Tukysa is a pill taken by mouth. The recommended starting dose of Tukysa is 300 mg twice a day, with or without food.
There are certain medicines, supplements, and foods you should not take or eat if you are taking Tukysa:
You should not take a type of medicine called a strong CYP3A inhibitor because it increases the effects of Tukysa. This class of medicines includes antifungal medicines such as Nizoral (chemical name: ketoconazole).
You should not take a type of medicine called a strong CYP3A inducer because it decreases the effects of Tukysa. This class of medicines includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis.
You should not take a class of medicines called P-glycoprotein substrates because Tukysa increases the effects of these medicines. This class of medicines includes Verelan (chemical name: verapamil), a calcium channel blocker used to treat high blood pressure and angina, and Ozurdex (chemical name: dexamethasone), a steroid used to treat arthritis and asthma.
It's important to know that women who are pregnant or planning to get pregnant should not take Tukysa. Tukysa can harm the developing fetus. If there is any chance you can become pregnant, you must use effective birth control while you're taking Tukysa and for at least 1 week after your last dose.
Visit Treatment for Breast Cancer During Pregnancy for more information.
Also, women who are breastfeeding or plan to breastfeed shouldn't take Tukysa. Together, you and your doctor will decide if you should take Tukysa or breastfeed.
Paying for Tukysa
If your doctor prescribes Tukysa and you have problems getting it covered by insurance or have problems paying for the treatment, Seattle Genetics, the company that makes Tukysa, may be able to help you.
SeaGen Secure, a personalized support program, will help eligible people navigate out-of-pocket assistance for the cost of the medicine, provide patient assistance and coverage support, and make connections to community resources and services. Call 855-4SECURE (855-473-2873) to talk to a SeaGen Secure representative.
Tukysa side effects
The most common side effects of Tukysa are:
Tukysa also may cause more serious side effects, including:
Severe diarrhea, which can cause dehydration, low blood pressure, and severe kidney problems. Tell your doctor about any diarrhea you have so it can be treated right away.
Liver problems, including elevated liver enzymes. Your doctor will check your liver function before you start taking Tukysa and every 3 weeks while you’re taking the medicine. Tell your doctor right away if you have yellowing of the skin or eyes, dark or brown urine, or bleed or bruise more easily than normal.
Tukysa (tucatinib) prescribing information. Seattle Genetics, Inc. Bothell, WA. 2020. Available at: https://seagendocs.com/TUKYSA_Full_Ltr_Master.pdf. (PDF)
— Last updated on April 1, 2022, 1:30 PM