Lapatinib is a cancer medication.

Lapatinib is used together with another medicine called capecitabine (Xeloda) or letrozole (Femara) to treat a certain type of advanced breast cancer that has spread to other parts of the body.

Lapatinib is often given after other cancer medications have been tried without successful treatment of symptoms.

Lapatinib may also be used for purposes not listed in this medication guide.

Do not use lapatinib if you are pregnant. It could harm the unborn baby.

Before you take lapatinib, tell your doctor if you have heart disease, liver disease, an electrolyte imbalance (low potassium or magnesium), or a personal or family history of Long QT syndrome.

To make sure you can safely take lapatinib, your heart function will need to be checked before you start treatment. Your liver function will need to be checked every 4 to 6 weeks during treatment.

Take lapatinib on an empty stomach.

Take this medication for the entire length of time prescribed by your doctor.

You should not use lapatinib if you are allergic to it.

To make sure you can safely take lapatinib, tell your doctor if you have any of these other conditions:

• heart disease;

• liver disease;

• an electrolyte imbalance (such as low levels of potassium or magnesium in your blood); or

• a personal or family history of "Long QT syndrome."

FDA pregnancy category D. Do not use lapatinib if you are pregnant. It could harm the unborn baby. Use effective birth control, and tell your doctor if you become pregnant during treatment.

It is not known whether lapatinib passes into breast milk or if it could harm a nursing baby. You should not breast-feed while you are taking this medication.