Biological markers – also known as biomarkers – are measurable biological characteristics that can provide indication of normal or abnormal biological processes. They are crucial in detecting disease presence and monitoring disease progression, including that of various cancers.
In this article, we review some biological markers that are used specifically in breast cancer diagnosis, and how they are integrated into cancer treatment to increase efficiency. From monitoring treatment response to assessing patient prognosis, biomarkers can help doctors make more tailored treatment strategies.
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Biological markers for breast cancer
Biomarkers can take various forms: enzymes, proteins, genetic biomarkers, RNA molecules, metabolites, and more. In the context of breast cancer, some common biomarkers are hormone receptors (oestrogen and progesterone), HER2, Ki-67, and the enzyme thymidine kinase (TK), to name a few.
Hormone receptors – such as oestrogen receptors and progesterone receptors – are proteins found on the surface of breast cancer cells. When activated by the hormones oestrogen and progesterone, they stimulate the growth and proliferation of cancer cells.
With the assessment of these hormone receptor statuses, doctors can determine the subtype of breast cancer and guide treatment decisions. For example, oestrogen-receptor positive breast cancers are typically more receptive to hormonal therapies such as tamoxifen or aromatase inhibitors, and patients that can benefit from these therapies can be identified.
HER2 stands for Human Epidermal Growth Factor Receptor 2. It is a protein that is involved in cell growth and division. In a subset of breast cancers, HER2 is overexpressed or amplified. Testing for HER2 status therefore can help determine the presence of certain breast cancer subtypes and eligibility for targeted therapies.
Ki-67 is a biomarker that reflects the tumour cell proliferation rate. A higher Ki-67 level indicates more aggressive tumour behaviour and higher likelihood of disease recurrence, which can influence the level and approach of cancer treatment required.
Ki-67 expression can also be evaluated to assess the response of tumours to neoadjuvant chemotherapy, which is a form of treatment administered before surgery to shrink tumours. A decrease in Ki-67 expression after treatment indicates a favorable response.
Thymidine kinase (TK)
Thymidine kinase (TK) is an enzyme involved in cell synthesis. It can serve as a biomarker in breast cancer, particularly in the form of thymidine kinase 1 (TK1). TK1 is found in dividing cells, including cancer cells, and its activity is closely linked to cell proliferation.
By measuring TK1 levels or activity in the breast tissue or in blood samples such as serum or plasma, important information about tumour growth and aggressiveness level can be determined. TK1 levels can also be used to assess treatment response in patients, so that doctors can evaluate the usefulness of certain forms of therapy. A decrease in TK1 levels after treatment may suggest a positive response, while unchanging or higher TK1 levels may indicate a lack of response.
Biomarkers in breast cancer treatment
Biomarkers play an important role in breast cancer diagnosis and treatment, from the early stages of detection to disease monitoring and prognostication.
Detection and diagnosis
Biomarkers can help in the detection and diagnosis of breast cancer. This is done through providing information about the presence or absence of the disease, as well as its specific characteristics, such as the cancer subtype. Biomarkers such as hormone receptors and HER2 status can define, for example, the molecular subtype of cancer.
Biomarkers can also be used to monitor the progression of breast cancer and assess an effective treatment response. For example, thymidine kinase activity in the breast tissue or blood can be measured over time to evaluate the development of the tumour or cancer cell proliferation.
Treatment approach and method selection
When biomarker levels are measured over time, it can give medical professionals insight into how quickly or slowly the cancer is developing and/or spreading. This can contribute to more informed treatment approaches and methods.
For example, by determining the status of hormone receptor oestrogen or progesterone, or HER2, medical professionals can decide between the choices of hormone therapy and HER2-targeted therapy. They can also make informed decisions in selecting the most appropriate chemotherapy agents based on the tumour’s genetic profile.
Risk assessment and prognostication
Finally, biomarkers help doctors assess the risk of breast cancer recurrence after successful treatment, offering insight into cancer prognosis. For example, using gene expression tests like Oncotype DX or PAM50, doctors can analyse gene activity in breast cancer cells and provide a risk score that helps predict the likelihood of recurrence.
The bottom line
Biological markers play a vital role in guiding the detection, diagnosis, and monitoring of breast cancer development. They also contribute to better treatment decisions by allowing medical professionals to better understand the nature of the cancer and each patient’s unique responses to treatment.
Specific biomarkers vary based on individual factors, such as cancer subtype and stage, which an experienced healthcare provider will know and be able to apply to different treatment journeys.