What are biomarkers?
Biomarkers are specific characteristics of cancer cells, such as protein expression or gene mutations. Some of the more commonly tested biomarkers include:
- Hormone receptors (HRs) – estrogen and progesterone
- HER2 (human epidermal growth factor receptor 2)
- BRCA1, BRCA2, PIK3CA, ESR1, AKT1, PTEN, and other gene mutations that may affect how your cancer grows or responds to certain therapies
What biomarker testing can tell you
These tests can help you and your care team better understand how rapidly the cancer may grow, what characteristics are driving its growth, and which treatments may be most effective.
Discuss your biomarker testing results with your care team, as the results may determine your eligibility for certain medicines or your ability to participate in clinical trials.
When to have your biomarker status checked
Some biomarker testing is done routinely after a breast biopsy—where a small portion of breast tissue or fluid is removed and analyzed for the presence of cancer cells, while others are done at different times after a breast cancer diagnosis. It is important to recheck the biomarker status of the tumor as the disease progresses, as it can change over time.
Questions to ask your doctor about biomarker testing
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Which biomarker tests do you recommend, and why?
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How will the biomarker tests be performed?
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How often do I need these tests?
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What do the results mean?
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What does it mean if my hormone receptor status and levels of HER2 expression of new tumors differ from the results of the original tumor?
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How will the results inform my treatment options?
What are the different subtypes of MBC?
There are several main subtypes of MBC, determined during biomarker testing for estrogen and progesterone hormone receptors (HRs) and HER2 status. These play a major role in guiding treatment decisions.
- Hormone receptor-positive (HR+): These are cancers that grow in response to the presence of hormone receptors like estrogen and/or progesterone.
- HER2-expressing: HER2 protein expression in a tumor exists on a spectrum from low levels of HER2 expression to an overexpression of the HER2 protein. Cancers with higher-than-normal levels of HER2 protein expression are considered HER2-positive.
- Triple-negative: These are cancers that grow in the absence of hormone receptors and without a higher-than-normal level of HER2 expression.
