Tukysa (Tucatinib): What to Expect, Side Effects, and More
If you’ve been diagnosed with advanced-stage HER2-positive breast cancer, your doctor may recommend Tukysa.
Tukysa can be used to treat metastatic HER2-positive breast cancer that has previously been treated with at least one anti-HER2 medicine. It can also be used to treat HER2-positive breast cancer that has spread to nearby tissue, but can’t be removed with surgery (called unresectable) and 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. Two of the most common tests are:
Tukysa is used in combination with Herceptin (chemical name: trastuzumab) and Xeloda (chemical name: capecitabine).
See Tukysa prescribing information.
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 receptor in cancer cells, which stops the cells from growing and spreading.
What to expect during Tukysa treatment
Tukysa is a pill taken by mouth. The recommended starting dose of Tukysa is 300 mg twice a day, with or without food.
You should avoid certain medicines and foods if you are taking Tukysa:
CYP3A4 inhibitors increase the effects of Tukysa. This class of medicines includes antifungal medicines such as Onmel (chemical name: itraconazole) and Biaxin (chemical name: clarithromycin), as well as antiretroviral drugs used to treat HIV such as Kaletra (chemical names: lopinavir and ritonavir).
CYP3A inducers decrease the effects of Tukysa. This class of medicines includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy.
Tukysa increases the effects of P-glycoprotein substrates. 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.
Tukysa side effects
Like most breast cancer medicines, Tukysa can cause side effects.
The most common side effects of Tukysa are:
Tukysa also may cause more serious side effects, including:
Severe diarrhea: Severe diarrhea 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: Your doctor will check your liver function before you start taking Tukysa and every three 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.
Pregnancy loss and birth defects: Tukysa can cause embryo death and birth defects. If you’re pregnant or planning to get pregnant, you shouldn’t take this medicine. You must use effective birth control while being treated and for one week after the last dose. You also shouldn’t take Tukysa while breastfeeding.
Real patient reviews
Members of our community discuss their experiences with Tukysa in the community forum. Here are some of their comments. Remember, it's essential to talk to your doctor about any side effects you're having and ask about ways to manage them.
“I get kadcyla every 3 weeks by infusion and take tucatinib every day. My [side effects] are fatigue ... loss of appetite, and sometimes I feel fluish several days after my infusions. My [medical oncologist] thinks the tucatinib is responsible for my lack of appetite.” — leftfootforward
“The Tukysa has been easy to tolerate, but we have to watch that liver enzymes don't elevate. Very grateful to have Tukysa that can pass the blood-brain barrier.” — rwhite
“So far, I have experienced only minor diarrhea with Tukysa that Imodium worked on well. Mostly depends on what I've eaten I think.” —Bliss58
Read more in our Tukysa discussion forum.
Paying for Tukysa
The cost of Tukysa may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use.
Note: Your insurance company may require you to get prior authorization before covering Tukysa.
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.
Learn more about financial assistance and medicine cost-lowering tips.
— Last updated on June 2, 2025 at 3:34 PM
