Targeted therapies for metastatic breast cancer

Targeted therapies can slow the growth and spread of cancer or control side-effects. They work by interfering with the biology of the cancer cells. 

The targeted therapies used most often for metastatic breast cancer
are:

Monoclonal antibodies

Monoclonal antibodies, for example, Trastuzumab (Herceptin®), Pertuzumab (Perjeta®) and antibody-drug conjugates trastuzumab emtansine and trastuzumab duruxetcan. These drugs are usually used for HER2-positive breast cancer. They target cancer cells that ‘overproduce’ or make too much of a protein called HER2. This protein is found on the surface of some cancer cells. The drugs work by attaching to the HER2 protein and slowing down or stopping the cancer cells' growth.

CDK4/6 inhibitors

CDK4/6 inhibitors are designed to interrupt enzymes that promote the growth of cancer cells. Types of CDK4/6 inhibitors commonly used in treating ER-positive, HER2-negative metastatic breast cancer are Palbociclib (Ibrance®), and Ribociclib (Kisqali®). Both of these drugs are usually given in combination with hormone therapy. Palbociclib and Ribociclib are given in tablet form.

PARP inhibitors 

PARP inhibitors can help stop cancer cells from repairing, which causes them to be too damaged to survive. You may be given a PARP inhibitor if your cancer is HER2 negative with an altered BRCA gene.

Cancer growth inhibitors

Cancer growth inhibitors block the chemical signals that trigger cancer cells to divide and grow. A cancer drug inhibitor used for metatstatic breast cancer is Lapatinib (Tyverb®).
 

Some drugs are given in tablet form. Others are given into a vein through a drip.

How does my doctor decide on which drugs to use?

Deciding which targeted therapy is best suited for you is determined
in a number of ways. 

One of the main factors is the biology of the tumour – looking at the cells to see if they have receptors and proteins on their surface that a particular therapy can target. For example, the HER2 protein. The cells are taken during a biopsy and looked at under the microscope. Biopsies from an area of secondary cancer may also be checked – it does not have to be a breast biopsy.

The majority of women with ER-positive, HER2-negative cancers are treated with CDK4/6 inhibitors and hormone therapy. About 1 in 5 women will have a HER2 positive breast cancer diagnosis.

Sometimes, if you had a HER2-positive breast cancer diagnosis and the cancer comes back, it may not be HER2-positive again. This is why biopsies on metastases are performed, to check the biology of the tumour.

Other deciding factors for targeted therapies can include:
• Previous treatments you have had
• How well you have tolerated side-effects
• Any other underlying health issues

There is ongoing research looking at different types of targeted drugs for metastatic breast cancer.

Side-effects of targeted therapy drugs

Side-effects of targeted drugs will vary depending on the particular drug you are taking. They can include:

• Allergic reaction – fever and chills
• Flu-like symptoms
• Nausea
• Headaches
• Diarrhoea
• Fatigue

Always contact your doctors if you experience any side-effects.

Read more about managing cancer side-effects