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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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SurgeryRadiotherapyChemotherapyHormone TherapyTargeted Therapy

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- (triple negative)

There are many different treatment options for HR-/HER2 metastatic breast cancer . Each targeted therapy works in a different way, but they all work to prevent the growth and division of cancer cells.

Type of treatment Action
Immunotherapy ​​​​​​​ Some immunotherapies work by inhibiting a protein that helps blood vessels around cancer cells to grow. The blood supply is needed to provide oxygen for the cancer to grow, so without it, the cancer cells can’t survive. Some other immunotherapies work by binding to a protein on cancer cells and causing an immune response by your own immune system.
PARP inhibitors Prevent the repair of damaged DNA, so prevent cancer cells repairing themselves.

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

How are HR-/HER2- targeted therapies given?

Immunotherapies are given intravenously at the hospital; this means the drug is given directly into your vein .

Immunotherapy is given in cycles of treatment. 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.

PARP inhibitors are taken orally as a tablet or a 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 chemotherapy ​​​​​​​. Your doctor will discuss what combination of treatments might be suitable for you.

Some immunotherapies can only be used for women or men with advanced breast cancer who express a protein called PD-L1  on their cancer cells.
PARP inhibitors can only be used for women or men with advanced breast cancer who have a fault in one of their BRCA genes ​​​​​​​.

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