Breast cancer remains one of the most important health challenges worldwide: an estimated 2.3 million new cases were diagnosed in 2020 alone. The complexity of this disease has prompted the development of innovative approaches to improve treatment and survival rates. One such approach is the use of biomarkers: biological indicators that provide valuable information about the nature of breast cancer. By identifying biomarkers, oncologists can predict outcomes and tailor treatment strategies to individual patients, ushering in a new era of precision medicine.
What are biomarkers in breast cancer?
Biomarkers are measurable indicators of biological processes or conditions that can be detected in tissues, blood, or other body fluids. In breast cancer, these markers offer a window into tumor biology, aiding in diagnosis, prognosis, and treatment selection.
Types of biomarkers
Breast cancer biomarkers They are generally classified into three categories:
- Diagnostic biomarkers: These help confirm the presence of cancer. For example, abnormal levels of CA 15-3 or CEA in blood tests may suggest breast cancer.
- Prognostic biomarkers: These predict the likely progression or outcome of the disease, such as risk of recurrence or survival rates.
- Predictive biomarkers: These guide treatment by indicating whether a patient will respond to a specific therapy, improving the effectiveness of care.
These markers can be genetic, protein-based, or metabolic and often reflect the unique characteristics of the patient’s tumor.
Biomarkers commonly used in breast cancer
Understanding the most commonly used biomarkers in breast cancer is essential to guide diagnosis, predict outcomes, and select the most effective treatment strategies.
Hormone receptor status
Hormone receptors, including estrogen receptors (ER) and progesterone receptors (PR), are among the most studied biomarkers of breast cancer.
- ER/PR positive tumors: These cancers depend on hormones for their growth, making them susceptible to hormonal therapies such as tamoxifen and aromatase inhibitors.
- ER/PR negative tumors: They are less likely to respond to hormonal therapies and often require alternative treatment strategies.
HER2/neu overexpression
HER2 is a protein that regulates cell growth. Approximately 15 to 20% of breast cancers overexpress HER2, which is related to aggressive disease progression.
- Therapeutic importance: HER2-positive patients benefit significantly from targeted therapies such as trastuzumab (Herceptin), pertuzumab, and lapatinib, which specifically inhibit HER2-driven tumor growth.
Ki-67 Index
The Ki-67 protein serves as a marker of cell proliferation.
- Low levels of Ki-67: They indicate slower growing tumors with a better prognosis.
- High levels of Ki-67: It suggests an aggressive cancer that may respond better to chemotherapy.
BRCA1 and BRCA2 mutations
BRCA1 and BRCA2 are tumor suppressor genes that, when mutated, significantly increase the risk of breast and ovarian cancer.
- Hereditary implications: Women with these mutations often follow preventive strategies, including prophylactic surgeries.
- Advances in treatment: PARP inhibitors, such as olaparib, are particularly effective in cancers associated with BRCA mutations.
Emerging biomarkers
Recent advances have introduced additional biomarkers, including:
- PD-L1 expression: A target for immunotherapy in triple negative breast cancer.
- PIK3CA mutations: It is found in ER-positive cancers, guiding the use of PI3K inhibitors such as alpelisib.
- Androgen receptor (AR): Investigated as a therapeutic target in specific subtypes of breast cancer.
Predict outcomes with biomarkers
Biomarkers play a critical role in understanding the likely trajectory of breast cancer.
Prognostic biomarkers
Prognostic markers help determine the natural history of cancer without intervention. For example:
- ER/PR-positive cancers: Generally associated with better outcomes due to the availability of effective hormonal therapies.
- HER2 positive cancers: Previously linked to poor outcomes, but now significantly improved with targeted therapies.
Predictive biomarkers
Predictive biomarkers identify patients most likely to benefit from a particular therapy. Examples include:
- HER2 status: Predicts response to trastuzumab and other HER2-targeted drugs.
- BRCA mutations: List the potential benefits of PARP inhibitors.
Adaptation of treatment with biomarkers
The ability to personalize treatment based on biomarker data has revolutionized breast cancer care.
Hormonal therapies
Patients with ER/PR-positive cancers can receive endocrine therapies, which block hormonal signals and inhibit tumor growth. Examples include:
- Tamoxifen: A selective estrogen receptor modulator.
- Aromatase inhibitors: Medications that reduce estrogen levels in postmenopausal women.
Targeted therapies
Targeted medications offer a focused treatment approach. For example:
- HER2-positive cancers are treated with trastuzumab, pertuzumab, or T-DM1.
- PI3K inhibitors are used in patients with PIK3CA mutations.
Multigene panels
Tests such as Oncotype DX and MammaPrint look at the expression of multiple genes to assess the risk of recurrence. These panels guide decisions about whether chemotherapy is necessary in early-stage cancers, sparing patients unnecessary side effects.
Biomarkers in immunotherapy
PD-L1 expression is increasingly used to identify immune checkpoint inhibitor candidates, particularly in aggressive subtypes such as triple-negative breast cancer.
Advanced technologies
The future of the application of biomarkers involves non-invasive techniques such as liquid biopsies. By analyzing circulating tumor DNA (ctDNA), doctors can monitor responses to treatment and detect recurrences earlier.
Conclusion
Biomarkers have revolutionized breast cancer treatment, allowing doctors to predict outcomes and personalize treatments like never before. From hormone receptor status to advanced liquid biopsies, these tools are essential to improving patient care and survival rates. As research continues to unlock the potential of breast cancer biomarkers, the promise of more effective, less invasive and equitable treatments becomes increasingly attainable.
For patients and healthcare providers, staying informed about the latest advances in biomarkers is crucial to navigating the complexities of breast cancer care.
