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Biomarkers 101

Welcome to Biomarkers 101! Maybe you’ve heard the term before but aren’t sure what it actually means. “What is biomarker testing? Did I have biomarker testing? What’s it for?” are common questions that come up. Want to hear it from the experts? Check out this engaging conversation with Dr. Sara Hurvitz and patient advocate Joanne Hiyashi.

The World Health Organization’s official definition of a biomarker is “any substance, structure or process that can be measured in the body or its products and influence or predict the incidence or outcome of disease.” This means that biomarkers can be found in the body or its tissues, blood and fluid. When measured, this information can show whether there may be disease or if anything is functioning abnormally.

As testing for biomarkers has expanded, it has given oncologists and researchers more tools to help their patients after a breast cancer diagnosis. Biomarkers are key to learning more about a patient’s tumor characteristics and overall risk.

What are some examples of biomarkers?

The main categories are:


  • Somatic cell mutations are not inherited. They occur after conception and are not passed through genes. Mutation to these cells can occur sporadically due to environmental causes, aging or lifestyle, for example.
  • These mutations are found by testing tumor cells.
  • An example is having extra copies of a gene that overexpresses the HER2 protein, which encourages the growth of cancer cells, or the PIK3CA mutation.


    • Germline mutations are inherited/genetic and are passed on at conception.
    • The mutation is found in an individual’s DNA sequence (found by blood or saliva testing) and is present in all cells.
    • An example is genetic testing for the BRCA 1/2 mutations.

    Genomic Sequencing:

    • This process sequences the genes of the tumor to look for mutations. This gives patients details that help decide their best course of treatment.

    Gene Expression Profiling:

      • Testing like Oncotype DX and MammaPrint can measure the activity of a tumor gene, which may show how likely it is for cancer to come back or spread. Your oncologist can use this information to determine how helpful certain treatments like chemotherapy may be.

      How is biomarker testing used in breast cancer diagnosis and treatment?

      When an individual is diagnosed with breast cancer, they will almost always have their tumor tested for biomarkers, such as HER2, estrogen-receptor and progesterone-receptor.

      • When diagnosed, a pathologist tests the breast cancer tumor for expressed proteins and hormone receptors, for example, which guides an individual’s prognosis and treatment plan.
      • Based on these results, an individual’s treatment would be used to block the pathways, in the case of ER and PR+, or target the over-expression of protein like HER2.

      Biomarker testing can lead to improved and more precise treatment options. For example, if an individual’s tumor tests positive for the presence of these biomarkers, they will likely be presented with the following therapies:

      • ER+ cancer cells: Treatments may include those that interfere with estrogen either by blocking the receptors as in tamoxifen or decreasing levels of estrogen. The latter is normally done with aromatase inhibitors or ovarian suppression medications.
      • Germline mutations: When breast cancer is associated with a genetic mutation like BRCA1 or BRCA2, PARP inhibitors (like olaparib or talazoparib) may be used to block cancer cells from repairing themselves. They are then less likely to grow and replicate.
      • Other biomarkers and medications may lead to a more personalized treatment approach, such as alpelisib (e.g. Piqray) in hormone-receptor positive MBC with a PI3 Kinase mutation and immunotherapy for triple-negative MBC with an overexpression of the protein PDL1.

      What is the use of biomarker testing in assessing risk of recurrence?

      • For Stage 1-3 breast cancer, genomic testing and biomarkers can be used to assess risk. Testing like Oncotype and MammaPrint, for example, may tell you your level of risk, which can also inform treatment options (for example, if your risk of recurrence is low, chemotherapy may not be recommended).

      What is the greatest benefit of biomarker testing for young adults specifically?

      • For any individual diagnosed with breast cancer under 50, genetic testing can provide great insight into the patient’s risk and treatment options. Young adults diagnosed with breast cancer have a higher rate of germline mutations, so it is important to assess family history and genetics.
      • Younger patients are more likely to be diagnosed with triple negative breast cancer or HER2 positive breast cancer. Tumor biomarker testing for ER/PR and HER2, as previously mentioned, will guide the individual’s treatment options and prognosis.
      • If an individual tests for ER+ breast cancer, they have treatment options which may block their estrogen receptors or lower the amount of estrogen in their body. These treatments can impact factors like early menopause and fertility. It is important to have these conversations with your oncologist before starting treatment to determine individual priorities and challenges.

      The future of biomarker testing has incredible potential to change the face of breast cancer. Young adults currently facing a breast cancer diagnosis and treatment are benefiting from biomarker testing. As researchers learn more, a greater number of young adults will be helped by new information and advances.

      Now that you have an overview of Biomarkers 101, we hope that you will take some time to learn more from our experts: explore the larger field of precision medicine with Dr. Nikhil Wagle and Victoria St. Martin, biomarkers and metastatic breast cancer with Dr. Reshma Mahtani and Dr. Yolanda Jameau, and questions to ask your healthcare team with Dr. Bora Lim and Miranda Gonzales through the YSC Biomarker Series.