Lapatinib (Tykerb) is targeted therapy in the dual tyrosine kinase inhibitor class. It is used with the chemotherapy pill capecitabine (Xeloda) or the aromatase inhibitor letrozole (Femara) to treat HER2-positive metastatic breast cancer after treatment with other medicines.


How lapatinib works

Lapatinib blocks the action of the HER2 protein from the inside the cell. You may be familiar with trastuzumab (Herceptin), a targeted therapy that also blocks the HER2 protein. While trastuzumab works on the outside of the cell, lapatinib works on the inside. This deprives the cancer cells of what they need to grow.

Because of the differences in how they attack cancer cells, lapatinib works in some HER2-positive cancers that stop responding to trastuzumab.


Who gets lapatinib

Lapatinib is given with capecitabine (Xeloda) to treat HER2-positive metastatic breast cancers that grow despite treatment with trastuzumab and other breast cancer medicines such as anthracyclines and taxanes.

Lapatinib may also be given in combination with the hormonal therapy letrozole (Femara). This combination is used to treat HER2-positive, hormone receptor-positive metastatic breast cancers in postmenopausal women.


How lapatinib is given

Lapatinib is available as pill. The standard dose is five tablets a day. If the treatment causes difficult side effects, your doctor may be able to reduce the number of pills you take each day.

You should take lapatinib at least one hour before or one hour after eating.


Side effects and things to remember

Eating grapefruit or products made with grapefruit may impact how well your body breaks down lapatinib, so avoid both while you are taking this medicine. Grapefruit contains a natural chemical, normally safe, that interacts with some medicines.

Common side effects from lapatinib may include:

If you are also taking capecitabine or letrozole, you could have side effects related to those medicines as well.

Before starting lapatinib, talk to your doctor about any heart and liver problems you have. Let your providers know about any medicines you are taking, including vitamins, herbal supplements and over-the-counter medicines.

Tell your doctor if you have side effects. If they are interfering with your everyday life, your doctor may be able to change your dose or switch you to another medicine. Seek medical help right away if you feel any chest pain. You should not become pregnant while you are taking lapatinib.

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on Side Effects for more information.


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Reviewed and updated: March 19, 2018

Reviewed by: Pallav K. Mehta, MD


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