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Understanding biomarkers

A biomarker is a substance within an organism in the body that can be measured to reveal if there are any abnormalities. Biomarkers are made by the tumour or by the body in response to the cancer. A biomarker may also be called a tumour marker and can be found in or on the tumour itself. Biomarkers help doctors learn more about a cancer and decide which treatment is best for you.

If you are diagnosed with breast cancer, your doctor may perform more tests. These tests are often performed on the tissue removed at the biopsy.

  • Hormone testing. Breast cancer cells that are estrogen receptor positive and/or progesterone receptor positive (ER+ and/or PR+) depend on hormones called estrogen and/or progesterone to grow. Testing for estrogen receptor and progesterone receptor status (ER and PR status) is done to find out if a cancer should be treated with hormonal therapy to stop these hormones from helping the cancer grow. Hormonal therapy may also be called endocrine therapy. In addition, hormonal therapy is sometimes combined with other types of treatments.

  • HER2 testing. Human epidermal growth factor receptor 2 (also known as HER2) is a gene everyone carries that controls protein on the surface of cells to help them grow. When a woman’s HER2 gene isn't working properly, it causes an overproduction of HER2 receptors (also known as HER2 protein overexpression) which can speed up breast cancer growth. Testing for HER2 is important because it helps a doctor know if the cancer can be treated with a targeted therapy designed to fight HER2 overexpression

  • Ki-67 and other markers may be used to test the tumour to measure the rate of cell growth, but there is currently no agreement between experts on how to make use of the results to make treatment decisions.

  • Genomic testing looks at the activity of certain genes in the body, such as the BRCA1 and BRCA2 genes. There are a number of tests to look at the genomics of the tumour that may be helpful in determining treatment or to determine a woman's risk of cancer recurrence in certain situations. These tests include Oncotype DX, Prosigna Breast Cancer Prognostic Gene Signature Assay (PAM 50) and mammaprint. These tests are performed on a tumour that has been removed. 

Biomarker tests can help doctors to:

  • Find cancer earlier
  • Improve diagnosis
  • Predict prognosis.  

Biomarkers and risk of recurrence

Biomarkers, such as HER2 or BRCA, can be a sign that cancer is at a higher risk of coming back. Many studies have shown that breast cancers that have an “over-expression” (producing too much) of HER2 have a poorer prognosis.

It should be noted that a patient’s HER2 status is just one part of the picture. There are other things that help doctors understand a patient’s prognosis, such as: 

  • Tumor size
  • Grade
  • Lymph node status (how many lympd nodes are affected by cancer)
  • Cancer type
  • Hormone status

Knowing a patient’s biomarkers is important because it will help doctors decide what treatments might work best on your type of breast cancer.