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What is metastatic breast cancer? ​​​​​​​ How do doctors make treatment decisions?SurgeryRadiotherapyChemotherapyHormone TherapyTargeted Therapy What matters most to you? Your doctor discussion guideYour questions answered
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How does targeted therapy work?

In order to understand how targeted therapies ​​​​​​​ work, it is important to understand that cancer cells are different from normal cells, because they divide and grow much faster than normal cells. These treatments work by targeting certain features of the cancer cells that help them grow in an uncontrolled manner.

Targeted treatments do this in a variety of different ways

Blocking the formation of new blood vessels for cancer cells

Stimulating the immune system ​​​​​​​ to destroy cancer cells

Inhibit proteins on or inside cancer cells that normally stimulate cancer growth

Inhibiting or halting the cancer's cell cycle

Delivering toxic substances in order to destroy cancer cells

In metastatic breast cancer, different treatments can be used to target the different subtypes of breast cancer. The following shows what targeted treatments can be used for each subtype of metastatic breast cancer.

Which targeted therapies are used for the different subtypes of breast cancer?

If your cancer is HR+/HER2+ or HR-/HER2+

There are many different treatment options for HR+/HER2+ or HR-/HER2+ metastatic breast cancer . For HER2+ breast cancer, these treatments all target cells displaying the HER2 protein receptor on their surface.

Type of treatment Action
Antibody-drug Conjugate The monoclonal antibody binds to a cancer cell and the combined drug enters the cell and prevents it from growing by interrupting the cell cycle. This combination destroys the cancer cell.
Monoclonal Antibodies Target (attach to) the HER2 ​​​​​​​ protein receptor on cancer cells and block its function, which stops cancer cells from growing.
Tyrosine Kinase Inhibitors Target (attach to) a HER2 protein receptor on cancer cells, preventing a protein from binding to it. This inhibits the protein and prevents it from causing the cancer cell to grow and divide.

The targeted treatments that are most suitable for you will depend on many factors, including whether you have received previous treatment for an earlier stage of breast cancer. Your doctor will discuss what treatment options are available to you.

How are HER2+ targeted therapies given

Antibody drug conjugates are given intravenously at the hospital, this means they are delivered directly into a vein . Monoclonal antibodies are usually given intravenously at the hospital as well. They can also be given as an injection under the skin.

Both of these treatments are given in cycles. The number of cycles you receive, and the length of time in between cycles, will vary dependant on the type of treatment. Your doctor will discuss this with you.

Tyrosine Kinase Inhibitors are taken orally as a tablet or capsule. These treatments are given continuously (e.g. you will take a tablet every day). Your doctor will discuss with you how your treatment should be taken and the length of time you may be on the treatment for.

Some targeted therapies are given in combination with another treatment such as hormone therapy ​​​​​​​ (if your cancer is HR+) or chemotherapy ​​​​​​​. Your doctor will discuss what combination of treatments might be suitable for you.

What are the side effects of targeted therapy?

Targeted therapies ​​​​​​​ can cause side effects. These will vary from person to person and will depend on the specific treatment. Talk to your doctor about the potential side effects of the treatments and what may be the best option for you.


The What’s Breast for Me? Campaign is funded by Pfizer Healthcare Ireland. Copyright © 2024 Pfizer Healthcare Ireland. All rights reserved. This site is intended for residents of the Republic of Ireland. The information provided on this site is intended for general information and education and is not intended to be a substitute for advice provided by a doctor or other qualified healthcare professional. All decisions regarding patient care must be made with a healthcare provider, considering the unique characteristics of the patients.


Date of preparation: January 2024