Understanding a Metastatic Breast Cancer Diagnosis and the Role of Biomarker Testing

Understanding a diagnosis of estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer should not only include the disease itself, but also the importance of biomarker testing and how results can inform a patient’s treatment plan, an expert said.

Dr. Gregory Vidal, director of clinical research at West Cancer Center and Research Institute in Memphis, chair of the breast oncology program at One Oncology and associate professor at University of Tennessee Health Science Center in Memphis, explained the characteristics of this disease, among other factors, during a session of CURE® Educated Patient® Updates in Metastatic Breast Cancer.

Breast cancer is a prevalent and complex disease that continues to be the subject of intense research and medical exploration. In particular, metastatic breast cancer is a term used to describe breast cancer that has spread from its original location in the breast to other parts of the body. It is a challenging form of cancer to treat, as the cells can adapt and resist treatment over time.

There are several different stages of breast cancer, from curable early-stage tumors (stages 0-3) to incurable metastatic breast cancer (stage 4). Hormone receptor-positive breast cancers, driven by estrogen and progesterone, tend to metastasize to organs like the bone, lung, liver and occasionally the brain.

The first key aspect is the importance of evaluating three crucial proteins in patients with breast cancer: ER, progesterone receptor and HER2. These receptors play a fundamental role in cancer development and growth. The presence or absence of these receptors in a patient's tumor affects their prognosis and available treatment options.

Treating Metastatic Breast Cancer

First-line treatment is the initial therapy given after a patient is diagnosed with metastatic breast cancer. Subsequent lines of treatment are used when the disease progresses or becomes resistant to the previous therapy, which is determined through close follow-up.

“We do monitoring through visits, through labs, through scans to determine how you're doing and whether or not the drug is still working,” Vidal explained.

He added that breast cancer cells are sometimes relentless even during treatment.

“What they're always trying to do is find a way to eventually overcome that resistance (to) that treatment that is being given to them,” Vidal said.

Consequently, metastatic breast cancer is considered incurable but treatable; although treatment can keep the disease in check, it cannot completely eradicate it.

When a patient’s disease no longer responds to a given treatment, it becomes necessary to switch to an alternative therapy. There is a range of treatment options available, some broad and others highly targeted. Targeted therapies aim to exploit specific genetic mutations or alterations in cancer cells, often resulting in higher efficacy and reduced side effects.

The Role of Next-Generation Sequencing

Biomarker testing, such as next-generation sequencing, is a critical component of metastatic breast cancer treatment. These tests examine the DNA of cancer cells to identify genetic mutations or alterations that are driving the cancer's growth. Understanding these biomarkers is essential because it enables the selection of the most appropriate treatment strategy. For instance, drugs are available to specifically target mutations like BRCA1 and BRCA2.

“Biomarkers essentially are the markers within the cell, the changes within the DNA that identifies this tumor (and) the reason this tumor continues to grow,” Vidal explained.

Biomarker testing can change over time as cancer cells adapt to treatment. In some cases, mutations may develop after exposure to previous therapies, such as the ESR1 mutation. This mutation alters the estrogen receptor, making it independent of estrogen for activation. Consequently, standard hormone-blocking therapies may not be as effective. However, specific drugs have been approved to target these mutated receptors effectively.

Vidal emphasized the importance of accurately identifying the type of breast cancer a patient has to tailor the treatment approach. The understanding of biomarkers and their role in cancer progression is crucial in guiding the choice of therapies, offering hope to those living with metastatic breast cancer.

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