Targeted drugs are a relatively new kind of treatment for breast cancer. Targeted therapy for breast cancer uses drugs directed at specific protein targets. Cancer cells need those proteins in order to grow and live longer. This way, targeted drugs treat cancer by killing or slowing the growth of breast cancer cells.

Many different types of targeted therapy can be used to treat breast cancer. If you have breast cancer, targeted therapy may be included in your treatment plan at any phase of treatment, before or after surgery.

What Is Targeted Therapy?

Cancer cells have mutations (changes in their DNA), which make them different from the normal cells in your body. These differences are usually caused by abnormal genes and other changes that control which proteins the cell makes and how the cell functions. These gene changes often allow cancer cells to grow out of control. Targeted drug therapies are directed at cancer cells’ proteins to destroy or slow their growth.

Targeted drugs are directed at proteins unique to cancer cells. That means these drugs do not affect normal cells in the same way as chemotherapy, which kills all fast-growing cells, regardless of whether they are normal cells or cancer cells.

When Is Targeted Therapy Recommended for Breast Cancer?

Targeted therapy can be used at any stage of breast cancer treatment, either before or after surgery. In some cases, targeted therapies may be taken for years as a long-term maintenance treatment to prevent the cancer from coming back. Some people take targeted therapy for years after other breast cancer treatments are complete.

Targeted therapy is used to treat several types of breast cancer, including:

• Hormone receptor-positive breast cancer — Cancer that tests positive for estrogen receptors (ER) and/or progesterone receptors (PR).
• HER2-positive breast cancer — Cancer with high levels of the HER2 protein, which promotes cell growth
• Breast cancer with BRCA gene mutations — Often associated with an increased risk of aggressive cancer types
• Triple-negative breast cancer (TNBC) — Cancer that is negative for ER, PR, and HER2, often more responsive to chemotherapy

Your doctor will make sure you are using the right targeted therapy for your type of cancer. They may test your blood or biopsy samples of your cancer to see if the specific target of the therapy is present in the cancer cell.

Targeted therapies may be used alone or in addition to other treatments, like chemotherapy or radiation therapy. In some cases, targeted therapy can work even when chemotherapy drugs don’t. Many targeted therapies are being used in the treatment of metastatic breast cancer, which is advanced breast cancer that has spread to other parts of the body.

How Is Targeted Therapy Taken?

Your treatment plan will depend on the type of cancer you have. Talk to your health care team about what to expect during your treatment.

Depending on the drug, targeted treatments may be taken as:

• A pill
• A shot given subcutaneously (under the skin)
• An intravenous infusion (into a vein, IV)

If you receive targeted therapy by a shot or IV, you may go to a cancer treatment center to receive your dose. If you receive targeted therapy by pill, you may be able to take it at home.

Depending on which targeted therapy you’re prescribed, you may take it every day, once a week, once a month, or sometimes less frequently.

Types of Targeted Therapy for Breast Cancer

Targeted therapy affects specific processes that are more common in cancer cells than in healthy cells.

Certain targeted therapies will trigger processes to stop cancer cells from growing or dividing. Others cause cancer cell death. Targeted drugs can also be attached to chemotherapy drugs to bring the chemotherapy directly to where the cancer is. If your doctor recommends targeted therapy, it’s because your care team identified that target on your breast cancer cells.

Monoclonal Antibodies

Monoclonal antibodies are proteins that are made in a laboratory. These antibodies are designed to target specific proteins in cancer cells.

For example, monoclonal antibodies can be targeted therapy for HER2-positive breast cancer. The HER2 protein affects how the cell grows. When monoclonal antibodies attach to HER2, they can stop cancer cells from growing.

Monoclonal antibody drugs used to treat breast cancer can be given by IV or subcutaneously and include:

• Margetuximab (Margenza)
• Pertuzumab (Perjeta)
• Trastuzumab (Herceptin)

Some monoclonal antibodies are also considered immunotherapy when they engage the immune system instead of cancer cells.

Antibody-Drug Conjugates

When a chemotherapy drug is attached to an antibody, it is called an antibody-drug conjugate (ADC). For breast cancer treatment, antibodies made to target HER2 can be attached to chemotherapy drugs to bring the chemo drugs directly to the cancer cells.

Examples of IV antibody-drug conjugates include:

• Ado-trastuzumab emtansine (Kadcyla)
• Fam-trastuzumab deruxtecan (Enhertu)
• Sacituzumab govitecan-hziy (Trodelvy)

Kinase Inhibitors

Kinases are proteins that act as messengers in cells, delivering messages to different parts of the cell. Kinase inhibitors are a class of drugs that block kinase activity. Kinase inhibitors are pills taken by mouth. Breast cancer therapy focuses on targeting kinases that are involved in cell growth. Blocking this process can slow down growth of breast cancer cells.

Your doctor may refer to some of these drugs by the type of kinase the drug targets. Some of the kinases that can be targeted in breast cancer include HER2, CDK4/6, mTOR, AKT, and PI3K.

Examples of kinase inhibitors that target HER2 include:

• Lapatinib (Tykerb)
• Neratinib (Nerlynx)
• Tucatinib (Tukysa)

CDK4/6 inhibitors include:

• Abemaciclib (Verzenio)
• Palbociclib (Ibrance)
• Ribociclib (Kisqali)

Everolimus (Afinitor) is an mTOR inhibitor. Capivasertib (Truqap) is an AKT inhibitor. Inavolisib (Itovebi) and Alpelisib (Piqray) are PI3K inhibitors.

PARP Inhibitors

Poly (ADP-ribose) polymerase (PARP) is a protein found in cells that helps damaged cells repair themselves. PARP inhibitors stop these proteins from doing their job so that cells can’t repair themselves.

People who have abnormal changes in the BRCA genes also have trouble repairing damage to those cells. When a person with a BRCA mutation takes a PARP inhibitor, their cancer cells can’t repair themselves and die. These medications are taken by mouth by people with a BRCA mutation and may eventually be recommended for people with other mutations like PALB2. Examples of PARP inhibitors include olaparib (Lynparza) and talazoparib (Talzenna).

Special Precautions When Taking Targeted Therapy by Mouth

Many targeted therapy drugs are available as pills that are taken by mouth and can be taken at home. Some targeted therapy drugs can be dangerous, so store your medication where others won’t come into contact with it. Make sure friends and family do not come into contact with your body fluids while you’re taking targeted drugs and for a time after you are finished.

Before starting a targeted drug therapy at home, ask your doctor or pharmacist questions about how to handle and store these drugs. Some questions include:

• Do I need to wear gloves to touch the pills?
• What precautions should I take to protect my friends and family?
• Do the pills have to stay in the bottle they came in?
• How do I dispose of the empty bottle?

Side Effects of Targeted Therapy

Like all drugs, even those you can buy over the counter, targeted drugs have side effects. Everyone is different — some people will have few or no side effects, while others may have serious problems. The side effects you experience depend on the type of treatment you are taking and the dose.

Talk to your cancer care team about the side effects specific to the targeted therapy you will be taking. Your doctor can recommend ways to prevent or manage the severity of many side effects.

Short-term side effects can start during treatment with targeted therapy and can go away over time after you finish your treatment. The amount of time it takes for side effects to improve is different for everyone.

Some of the common side effects of targeted drugs are similar to those of chemotherapy. They are usually short-term, including:

• Skin changes
• Nausea or vomiting
• Liver problems
• Diarrhea or constipation
• Mouth sores
• Trouble breathing
• Fatigue
• Cough
• Headache
• Hair loss
• Increased risk of infection

Some people can have serious side effects when taking targeted drugs. Possible side effects include:

• High blood pressure
• Bleeding or clotting problems
• Slow wound healing
• Heart damage
• Vision problems
• Autoimmune reactions
• Swelling

Your cancer care team will monitor you closely to check for side effects. Let your doctor know about any changes in how you feel during and after your treatment.

Long-Term Side Effects

Targeted drugs are still new, so researchers are still learning whether there may be long-term side effects. Scientists do know that some side effects of cancer treatment, like heart damage caused by chemotherapy, can last a lifetime. More information on long-term side effects may emerge as ongoing clinical trials are completed.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 74,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you taken a targeted drug therapy for breast cancer? Share your experiences in the comments below, or start a conversation by posting on your Activities page.