Targeted therapy for metastatic breast cancer

Targeted therapy, also called biological or biologic therapy, is treatment that blocks the growth and spread of cancer cells.

Targeted therapy interferes with processes in cells that help cancer grow, such as targeting a protein that allows the cancer to grow quickly or in an abnormal way.

Some targeted therapies work like the antibodies in our immune system. Targeted therapies are less likely to affect normal cells than other treatments.

Hormone positive

How do targeted therapies work for hormone-positive metastatic breast cancer?

The well known targeted therapies for breast cancer are the hormone-blocking therapies that target oestrogen receptors. Several different hormone-blocking therapies are available, including tamoxifen, anastrozole, letrozole and exemestane.

Each works to block the effect of oestrogen in one of two ways: 

• attaching to the oestrogen receptors on breast cancer cells so that oestrogen cannot enter the cells and help them grow
• lowering the amount of oestrogen circulating in the body.

The CDK 4/6 inhibitors – palbociclib (Ibrance), ribociclib (Kisqali) and abemaciclib (Verzenio) – are also examples of targeted therapies for the treatment of hormone receptor-positive, HER2-negative metastatic breast cancer. The CDK inhibitors work by blocking the function of enzymes in the pathway that helps control how cells grow and divide.

These enzymes are commonly found in higher-than-normal amounts in breast cancer cells. These targeted treatments can be combined with hormone-blocking treatments to increase their effectiveness and extend length of control.

HER2 positive

How do targeted therapies work for HER2-positive metastatic breast cancer?

The HER2 therapies that block the action of HER2 receptors on cells are examples of targeted treatments. Several HER2 therapies are available, including trastuzumab, pertuzumab (Perjeta), trastuzumab emtansine (Kadcyla), lapatinib (Tykerb) and – more recently – trastuzumab deruxtecan (Enhertu), which is currently recommended for Pharmaceutical Benefits Scheme (PBS) subsidy.

Breast cancers that are HER2 positive have excessive numbers of HER2 receptors on the surface of the cancer cells. These receptors allow growth factors to stimulate the growth of the cancer cells. 

Treatments that block the HER2 receptors prevent this growth stimulation, in turn, controlling the cancer.

Triple negative

How do targeted therapies work for triple negative metastatic breast cancer?

Targeted treatments are also available for some triple negative metastatic breast cancers. These include Sacituzumab govitecan (Trodelvy) and pembrolizumab (Keytruda).

Trodelvy belongs to a class of drugs called “antibody-drug conjugates.” It is made up of an antibody and a chemotherapy drug that work together to treat the triple negative breast cancer. It is a targeted therapy that delivers chemotherapy directly into the cancer cells.

The use of Trodelvy has been approved for Australians who have had at least two previous systemic treatments (e.g. chemotherapy) for triple negative breast cancer. At least one of those treatments must have been for metastatic disease.

Keytruda is an “immunotherapy” (checkpoint inhibitor) drug that targets PD-1, a protein on T cells that normally helps keep them from attacking other cells in the body. By blocking PD-1, this drug boosts the immune response against breast cancer cells. 

Keytruda is now available on the PBS for metastatic triple negative breast cancer. Read more about immunotherapies.

Access to treatments

Targeted therapies not currently available for metastatic breast cancer (i.e. not listed on the PBS) may be accessible through a clinical trial or patient access scheme.

Clinical trials

New targeted therapies that block other pathways within cancer cells are currently in development. Ask your doctor about newer treatments that may be available to you through a clinical trial.

Patient access programs

You might learn of drugs available to treat breast cancer that are not subsidised through the PBS. Some pharmaceutical companies have access programs to help lower the cost of treatments not available on the PBS.

Sometimes, treatment is available free of charge for people who meet specific criteria.

The best way for you to find out if this an option for you is to ask your doctor. Your doctor can check the Medicines Access Portal or contact the relevant pharmaceutical company.

Side effects

Managing symptoms and side effects contains information on dealing with certain side effects from various forms of treatment for metastatic breast cancer, including targeted therapies.