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Understanding MBC > What is a Biomarker?

What is a Biomarker?

A biomarker is a substance found in blood, urine, or other body fluids. It can also be found in or on the tumor and is made by the tumor or by the body in response to the cancer, thus providing doctors useful information about a cancer.1 In breast cancer, biomarkers give such important information that they are often used to describe cancer subtypes.2

Identifying biomarkers can help your doctor know which treatments might work best for a specific cancer.2,3 They can also determine how well treatment is working, or signal if cancer is returning.1,10,11 Important biomarkers in breast cancer are hormone receptors (HRs), HER2, and PIK3CA.1,4,5,12

Types of biomarkers


How will my doctor know my biomarkers?

A biomarker may be found or measured by testing blood or tissue.5 Biomarker testing may be done when your doctor first discovers that the cancer has spread (metastasized). Testing can also be done when the cancer starts to grow or spread again after a treatment is given (also called progression), if it was not done earlier.5,7


Download this brochure to learn more about MBC and the role that biomarkers play in treating it.


  1. American Society of Clinical Oncology. Biomarkers to guide treatment for early-stage breast cancer. recommendations-patients/biomarkers-guide-treatment-early-stage-breast-cancer. Accessed September 25, 2019.
  2. National Cancer Institute. Breast cancer treatment (PDQ®)–health professional version. Accessed December 2, 2016.
  3. National Cancer Institute. Tumor markers. cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet. Accessed November 27, 2019.
  4. US National Library of Medicine. PIK3CA gene. Genetics Home Reference. Accessed September 25, 2019.
  5. My Cancer Genome. PIK3CA. Accessed December 5, 2019.
  6. HER2 status. Accessed June 18, 2019.
  7. American Cancer Society. Caregiver resource guide. 2019. flyers/american-cancer-society-caregiver-resource-guide.pdf. Accessed November 4, 2019.
  8. American Cancer Society. Targeted therapy for breast cancer. cancer.html. Accessed September 24, 2019.
  9. National Cancer Institute. Biomarker. NCI Dictionary of Cancer Terms. Accessed October 25, 2019.
  10. Karley D, Gupta D, Tiwari A. Biomarker for cancer: a great promise for future. World J Oncol. 2011;2(4):151-157.
  11. American Society of Clinical Oncology. Use of biomarkers to guide decisions on systemic therapy for women with metastatic breast cancer: American Society of Clinical Oncology Clinical Practice Guideline. Accessed December 9, 2019.
  12. Blood marker tests. Diagnosing and Monitoring Breast Cancer Accessed December 9, 2019.
  13. Aromatase inhibitors. Accessed July 30, 2020.
  14. National Cancer Institute. Breast cancer treatment (PDQ®)–patient version. Accessed June 26, 2019.
  15. American Cancer Society. Targeted therapy for breast cancer. Accessed September 24, 2019.