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Understanding MBC > 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
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). 6 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