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What is HER2 positive breast cancer?

Understanding HER2 positive breast cancer

There are many different types of breast cancer. If you’re diagnosed with HER2 positive breast cancer, this means your cancer cells have higher than normal levels of HER2.

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. These cancer cells often grow and spread faster than other breast cancers, but also 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.

Around 15-20% of all breast cancers are HER2 positive. HER2 positive breast cancer is also more common in younger women below the age of 60.

How are tumours tested for HER2?

Following a diagnosis of invasive breast cancer, the cancer will be tested for HER2. This involves 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 and in situ hybridisation (ISH) test.

Immunohistochemistry (IHC) test

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

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 if the cancer is HER2 positive or HER2 negative. If the results are inconclusive another ISH test will be conducted.

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

What is the treatment for HER2 positive breast cancer?

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 (Kadcyla)
Lapatinib (Tykerb)
Neratinib (Nerlynx)
Other newer agents, i.e. trastuzumab deruxtecan

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

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

ReferencesReferences

For a full list of references, click here.

American Cancer Society. (2019). Breast cancer HER2 status. Retrieved on 20 March 2020 from https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/breast-cancer-her2-status.html
Mayo Clinic. (2018). HER2 positive breast cancer: What is it. Retrieved on 20 March 2020 from https://www.mayoclinic.org/breast-cancer/expert-answers/faq-20058066

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