Breast cancer biomarkers are important in guiding treatment decisions and predicting outcomes. Among these biomarkers, Human Epidermal Growth Factor Receptor 2 (HER2), Estrogen Receptor (ER), Circulating Tumor DNA (ctDNA), and Progesterone Receptor (PR) are particularly important in breast cancer diagnosis, prognosis, and therapeutic targeting.

In this article, we will look at these four biomarkers and how they can be used in the monitoring of breast cancer disease progression and treatment.

Human Epidermal Growth Factor Receptor 2 (HER2)

HER2 is a protein that promotes cellular division and growth. In normal breast cells, HER2 helps regulate cell growth, but in some breast cancers, the HER2 gene is overexpressed, leading to increased production of HER2 protein. This overexpression can result in aggressive tumor growth and poorer prognosis. HER2-positive breast cancer accounts for about 20-25% of all breast cancer cases.

The detection of HER2 overexpression is crucial in determining treatment options for breast cancer patients. HER2-targeted therapies, such as trastuzumab (Herceptin), pertuzumab, and ado-trastuzumab emtansine (Kadcyla), specifically target HER2-positive breast cancer cells, which inhibit their growth and proliferation. These targeted therapies have revolutionized the treatment landscape for HER2-positive breast cancer, significantly improving outcomes and survival rates.

Estrogen Receptor (ER)

Estrogen Receptor (ER) is a protein that binds to estrogen, a hormone that promotes the growth of some breast cancers. In ER-positive breast cancer, tumor cells have receptors for estrogen that allow estrogen to stimulate their growth. ER-positive breast cancer is the most occurring subtype, which accounts for approximately 75% of all breast cancer cases.

Detection of ER expression is important in determining the treatment approach suitable for breast cancer patients. Hormone therapy, such as tamoxifen, aromatase inhibitors (e.g., letrozole, anastrozole, exemestane), and selective estrogen receptor degraders (e.g., fulvestrant), targets ER-positive breast cancer cells, blocking estrogen’s effects and inhibiting tumor growth. These hormone therapies have proven highly effective in reducing the risk of recurrence and improve survival in ER-positive breast cancer patients.

The combination of HER2 and ER status further refines breast cancer subtyping and treatment decisions. Breast cancers that are both HER2-positive and ER-positive are classified as “HER2-positive/ER-positive” and may benefit from a combination of HER2-targeted therapy and hormone therapy. Conversely, triple-negative breast cancers lack expression of HER2, ER, and progesterone receptor (PR) and require alternative treatment approaches, such as chemotherapy.

Circulating Tumor DNA (ctDNA)

In the management of breast cancer, circulating tumor DNA (ctDNA) has shown great industry as a noninvasive biomarker for evaluating the course of the illness. It is also vital to the effectiveness of treatment and the possibility of recurrence. ‘ctDNA’ describes broken-up DNA that tumor cells release into the circulation. This DNA offers an image of the tumor’s genetic changes and heterogeneity.

Blood samples from individuals with breast cancer can show the presence of ctDNA, even in the early stages of the illness. The discovery of ctDNA using liquid biopsy enables less invasive diagnosis and disease progression tracking. Furthermore, ctDNA analysis may help determine specific genetic mutations or variations linked to breast cancer subtypes, directing therapy choices and prognostic estimations.

ctDNA helps monitor breast cancer progression. For example, tumor shrinkage and therapeutic response may be correlated with reductions in ctDNA levels after treatment starts. Conversely, persistent or rising ctDNA levels indicate disease progression or resistance to therapy, which calls for a change in approach.

ctDNA analysis also offers risk stratification and predictive data for breast cancer patients. Tumor mutational frequency, copy number changes, and clonal evolution are among the ctDNA features linked to overall survival outcomes and recurrence risk. Hence, ctDNA checks enable prompt action to stop the course of the illness by allowing early diagnosis of metastasis or recurrence.

Progesterone Receptor (PR)

Treatment decisions for breast cancer are decided by the PR status as well as the status of the ER, HER2, and other essential biomarkers associated with the disease. Progesterone receptors can either be present or absent in breast cancer, and this can affect how the cancer cells behave and react to hormone treatment.

Usually, hormone-sensitive, PR-positive breast cancer may react to hormone treatment with drugs like aromatase inhibitors or tamoxifen. By preventing estrogen and progesterone from acting on cancer cells, hormone treatment slows the development of tumors and lowers the chance of recurrence. Hormone treatment aimed at progesterone receptors has little effect on PR-negative breast cancer cells. Instead, depending on other tumor features and genetic subtypes, these cancers may need alternate treatment modalities such as chemotherapy, targeted therapy, or immunotherapy.

Furthermore, patients with PR-positive tumors frequently have better results and prognoses than those with PR-negative tumors. PR positivity is linked to better survival rates, decreased recurrence risk, and slower tumor development.

Final words

Clinicians can monitor the activity and levels of different biomarkers to track the progression of breast cancer, gauge the effectiveness of treatment, and identify any possible recurrences early on in disease follow-up and treatment. By targeting the biomarkers mentioned in this article, clinicians can then tailor treatment strategies to individual patients, which can optimize outcomes and improve survival rates in breast cancer. Ongoing research continues to explore targeted therapies and novel biomarkers to identify new tests for breast cancer monitoring, in the hopes to further advance precision medicine in this field of cancer care.