• Developed and funded by Pfizer Ltd
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
  • AAA+
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-

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
CDK 4/6 inhibitors Inhibit enzymes ​​​​​​​ (called CDK 4 and CDK 6) that normally control the cell cycle in all cells of our bodies. This stops the cancer cells from dividing and growing.
mTOR inhibitors Inhibit a protein (called mTOR) involved in cell division and the growth of blood vessels that supply the cancer with oxygen, so the cancer cells can’t survive.
PARP inhibitors Prevent the repair of damaged DNA, so prevent cancer cells repairing themselves.
PI3K inhibitors Inhibit a protein (called PI3K) involved in regulating cell division and growth, so prevent the cancer cells from dividing and growing.

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?

Targeted therapies ​​​​​​​ for HR+/HER2- breast cancer are given orally as a tablet or a capsule. Some treatments are given continuously (e.g. you will take a tablet every day) or some are given in cycles. Your doctor will discuss with you how your treatment should be taken and the length of time you may be on the treatment for.

CDK 4/6 inhibitors, mTOR inhibitors and PI3K inhibitors are given in combination with a hormone therapy , whilst PARP inhibitors are given alone. Your doctor will discuss what combination of treatments might be suitable for you.

PARP inhibitors can only be used for women or men with secondary breast cancer who have a fault in one of their BRCA genes ​​​​​​​. If your breast cancer is HR+, PARP inhibitors may only be an option after treatment with a hormone therapy.​​​​​​​

PI3K inhibitors can only be used for women or men with secondary breast cancer who have a PI3KCA mutation in their genes. They may only be an option after treatment with a certain hormone therapy.

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.​​​​​​​

Click here to learn more about the side effects of targeted therapy.


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