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.
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.
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
- menopausal symptoms
- redness and tingling in the hands and feet
- skin changes
- nausea and vomiting
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.