Tucatinib

Say it: too-KA-tih-nib · Brand names: Tukysa

Tucatinib is a targeted therapy pill that blocks HER2, a protein that helps some cancers grow.

What it is

Some cancer cells have too much of a protein called HER2 on their surface. HER2 sends signals that tell the cells to grow. Tucatinib blocks these signals from inside the cell and is used along with other cancer medicines.

Often used for

• HER2 positive breast cancer that has spread, including to the brain
• HER2 positive colon or rectal cancer that has spread

How you get it

Tucatinib is a pill you take by mouth at home, twice a day, about 12 hours apart. You can take it with or without food. It is given along with other cancer medicines. Your schedule may be different.

Common side effects and what helps

• Diarrhea. Drink plenty of fluids. Tell your team early, since they may give you medicine to help.
• Redness, soreness, peeling, or blisters on the palms of your hands or soles of your feet. Use thick lotion, wear soft shoes, and avoid hot water.
• Feeling sick to your stomach or throwing up. Eat small meals and ask your team about anti-nausea medicine.
• Feeling tired or weak. Rest when you need to, and try short walks.
• Mouth sores. Brush gently with a soft toothbrush and rinse with a mild salt water rinse. Avoid spicy foods.
• Not feeling hungry or losing weight. Try small, frequent meals and snacks.
• Rash. Use gentle soap and fragrance free lotion.

Call your care team right away if you have

• Diarrhea that does not get better with the medicine your team gave you, or more than 4 to 6 loose stools in a day
• Feeling dizzy or faint, or not able to keep fluids down
• Yellow skin or eyes, dark tea colored urine, or pain on the right side of your belly
• Itching all over your body, or bleeding or bruising more easily than normal
• A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or chills

Before you start, tell your team

• If you are pregnant, may become pregnant, or are breastfeeding
• If you have liver problems
• All the medicines, vitamins, and herbal products you take, since some can change how this medicine works

Good to know

• Diarrhea can be severe. Your team may give you medicine to keep at home for it.
• It can harm the liver. You will have blood tests to check your liver often.
• It can raise a kidney blood test (creatinine) even when your kidneys are working normally. Your team will look at this.
• This medicine can harm an unborn baby. Use birth control during treatment and for some time after. Ask your team how long.

At home

• Take the pills at about the same times each day, with or without food.
• Swallow the pills whole. Do not chew, crush, or split them.
• If you miss a dose or throw up after taking it, ask your team what to do. Do not take extra pills to make up for it.
• Keep the pills in the original bottle with the drying packet inside. Ask your pharmacist how long the bottle is good for after you open it.
• Store at room temperature, away from children and pets.

Questions to ask

• How long will I take this medicine?
• What should I do at the first sign of diarrhea?
• Is it safe to take my other medicines, vitamins, or supplements with this one?
• How will we know if this medicine is working?

Side effect guides

• Fatigue (tiredness)
• Nausea and vomiting
• Diarrhea
• Mouth sores
• Skin rash (including EGFR-inhibitor rash)
• Hand-foot syndrome

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.