Targeted therapy works differently than chemotherapy. The side effects of targeted therapy drugs are often different and less severe than those of standard chemotherapy drugs.

One out of five breast cancers have an overabundance of the protein HER2/neu (American Cancer Society, 2015b). Certain drugs target this protein to prevent it from fueling cancer growth.

The possible side effects associated with targeted therapy drugs are generally mild but include:

Heart damage: Treatment with anti-HER2/neu drugs can lead to heart damage. For the majority of women, the effect is short term and goes away once treatment has stopped. Nevertheless, patients should speak with their physician immediately if they experience any shortness of breath, swelling of the legs or feet, or trouble with any physical activity.
Fetal damage or death: Women who are pregnant should not be treated with any of these drugs for risk of harming the fetus. It is very important that women who could potentially become pregnant during treatment discuss effective methods of birth control with their physician first.
Other targeted therapy drugs are used to aid hormone therapy drugs in treating hormone receptor-positive breast cancer. They are also used with hormone therapy drugs to treat women with advanced breast cancer. They are meant to be used once the initial hormone therapy drugs are no longer working effectively. Possible side effects include cough, diarrhea, feeling weak or tired, fatigue, low blood counts, mouth sores, nausea, and shortness of breath. Taking these drugs can also affect certain lab exams, so a patient’s physician may need to check blood work from time to time.