Targeted drug therapies for breast cancer are also systemic treatments that attack a specific abnormality on the breast cancer cells.  Targeted drug therapies, similar to chemotherapy and hormone therapy, can be given before surgery (neoadjuvantly), after surgery (adjuvantly), or to treat recurrences or metastases to other organs. Unlike chemotherapy drugs, targeted therapies usually do not attack normal cells in the body.

HER2 Therapies

HER2, also known as human epidermal growth factor receptor 2, is a protein that when overexpressed on cancer cells promotes cancer cell growth. HER2-positive cancers tend to be more aggressive, but the treatments that are now available to target HER2 are so effective that the prognosis for patients with these tumors is very good. 

Trastuzumab (Herceptin)

Trastuzumab is an antibody against the HER2 protein.  It is given to patients as an intravenous (IV) infusion.  In some situations it is given in combination with chemotherapy drugs. It is usually given every 3 weeks for a full year when treating a patient around the time of surgery. For patients who develop HER2-positive metastases, it can be given indefinitely.

Pertuzumab (Perjeta)

Pertuzumab is a newer antibody against the HER2 protein. It is given in combination with trastuzumab and chemotherapy drugs for patients undergoing neoadjuvant treatment prior to surgery. Pertuzumab has also been approved for the treatment of metastatic HER2-positive breast cancers. Similar to trastuzumab, it is given intravenously every 3 weeks.

The other agents against HER2 are lapatinib (Tykerb), which is given in pill form, and ado-trastuzumab emtansine (Kadcyla), which is given intravenously.

The following are some of the side effects of these medications:

• Nausea
• Fever
• Muscle aches
• Chills
• Diarrhea
• Hair loss
• Neuropathy
• Hand-foot syndrome
• Congestive heart failure

Although the risk of congestive heart failure is low, if you are placed on these medications your heart will be monitored closely with either an echocardiogram or MUGA scan before treatment and every few months while on the medications. 

mTOR Inhibitors

Everolimus (Afinitor) is a drug that blocks the mTOR protein on cancer cells. It is used along with exemestane (Aromasin) to treat hormone-positive cancers that have grown while on anastrozole or letrozole.  Everolimus is a pill that is taken daily.

The following are the most common side effects of everolimus:

• Fatigue
• Nausea
• Diarrhea
• Cough
• Mouth sores
• Increased risk of infection

Kinase Inhibitors

Palbociclib (Ibrance) is a drug that blocks 2 proteins in cells: cyclin-dependent kinase (CDK) 4 and 6. It is prescribed with an aromatase inhibitor to treat patients with advanced hormone-positive cancers. Palbociclib is given as a pill that is taken every day for 3 weeks with a week off before starting the cycle again.

The following are the most common side effects of palbociclib:

• Fatigue
• Nausea
• Diarrhea
• Hair loss
• Mouth sores
• Anemia