What is HER2 positive breast cancer?

HER2 stands for human epidermal growth factor receptor 2. The HER2 proteins are found on the outside of breast cells and promote the growth of cancer cells. Cancer cells with higher than normal levels of HER2 are known as HER2- positive. These cancer cells often spread and grow faster than other breast cancers, but are also seen to respond well to treatments that directly target the HER2 protein.¹ The status of your HER2 can help determine how aggressive the cancer is and what treatment will be most suitable.

Women who have been diagnosed with invasive breast cancer will be tested for HER2. This involves either a biopsy to obtain a sample of the cancer for testing. A biopsy is a safe procedure that can usually be performed at a doctor’s clinic under local anaesthetic. There are two types of tests:

Immunohistochemistry (IHC) test

IHC will test the presence of over-expression HER2 protein receptors. A pathologist looks at the tissue sample under a microscope. Results of:

• 0 is negative
• 1+ is negative
• 2+ is considered uncertain
• 3+ is positive

If the test comes back as 2+ you may be required to have more tests, such as in-situ hybridisation (ISH)

In situ hybridisation (ISH) test

This test looks at the genetics of the cancer sample to confirm in the cancer is HER2 positive or HER2 negative. If the results are inconclusive often an IHC test will be conducted, and/or another ISH test, or new samples may be required.

Being tested for overexpression of HER2 is important so your care team can determine the best course of treatment.

Although HER2-positive breast cancer is commonly an aggressive form of cancer, it does respond well to many treatments such as targeted therapy that specifically target the HER2 protein and some standard chemotherapy regimens. Some of these treatments include²:

• Trastuzumab (Herceptin)
• Pertuzumab (Perjeta)
• TDM-1
• Lapatinib (Tykerb)
• Neratinib (Nerlynx)
• Other newer agents, i.e. trastuzumab deruxtecan

For patients with HER2-positive breast cancer that is also estrogen and progesterone-positive, hormonal therapy in addition to HER2 targeting therapies is also an effective treatment.

Understanding your diagnosis and being comfortable with your treatment is important. Don’t be afraid to ask your oncologist any questions so you feel supported at each step.