Some women with breast cancer may receive drugs called targeted therapy. Targeted therapy uses drugs that block the growth of breast cancer cells. For example, targeted therapy may block the action of an abnormal protein (such as HER2) that stimulates the growth of breast cancer cells. (For information about HER2, see Lab Tests with Breast Tissue.)

Trastuzumab (Herceptin®) or lapatinib (TYKERB®) may be given to a woman whose lab tests show that her breast tumor has too much HER2:

• Trastuzumab: This drug is given through a vein. It may be given alone or with chemotherapy. Side effects that most commonly occur during the first treatment include fever and chills. Other possible side effects include weakness, nausea, vomiting, diarrhea, headaches, difficulty breathing, and rashes. These side effects generally become less severe after the first treatment. Trastuzumab also may cause heart damage, heart failure, and serious breathing problems. Before and during treatment, your doctor will check your heart and lungs. The NCI fact sheet Herceptin® (Trastuzumab) has more information.
• Lapatinib: The tablet is taken by mouth. Lapatinib is given with chemotherapy. Side effects include nausea, vomiting, diarrhea, tiredness, mouth sores, and rashes. It can also cause red, painful hands and feet. Before treatment, your doctor will check your heart and liver. During treatment, your doctor will watch for signs of heart, lung, or liver problems.

You may want to ask your doctor these questions before having hormone therapy, chemotherapy, or targeted therapy:

• What drugs will I be taking? What will they do?
• When will treatment start? When will it end? How often will I have treatments?
• Where will I have treatment?
• What can I do to take care of myself during treatment?
• How will we know the treatment is working?
• Which side effects should I tell you about?
• Will there be long-term effects?
• How often will I need checkups?