Understanding Breast Cancer Biomarkers Drives Patient Treatment Decisions

Dr. Mabel Mardones educates patients on breast cancer updates: © stock.adobe.com.

It is crucial to understand the characteristics of the disease following a diagnosis of metastatic breast cancer, especially the cancers subtypes and associated biomarkers, as these directly impact the direction of treatment decisions. Moreover, advancements in treatment strategies within the therapeutic landscape aims to manage disease, control progression, as well as maintain quality of life for patients.

At a CURE® Educated Patient® Metastatic Breast Cancer Updates event, which was held in tandem with Rocky Mountain Cancer Centers, Dr. Mabel Mardones led a variety of discussions around understanding metastatic breast cancer and its subtypes. Notably, she focused on estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer.

“[One takeaway is] just understanding a lay of the land as to how a medical oncologist thinks and some updates in ER-positive metastatic disease, such as learning about staging and [circulating tumor cells], minimal residual disease scans, targeted options, [and more],” she explained.

Mardones is a board-certified medical oncologist and hematologist with a sub-specialty of expertise in breast cancer.

Breast Cancer Biomarkers

Breast cancer is a heterogeneous disease, meaning it presents with diverse characteristics among different patients.

The primary subtypes of breast cancer are defined by the presence or absence of specific receptors on the surface of the cancer cells, including:

• Hormone receptor (HR)-positive breast cancer: This includes ER-positive and/or progesterone receptor (PR)-positive breast cancer. These cancers are fueled by the hormone’s estrogen and/or progesterone.
• HER2-positive breast cancer: These cancers have an overexpression of the human epidermal growth factor receptor 2 protein, which promotes cell growth.
• Triple-negative breast cancer (TNBC): These cancers lack expression of estrogen receptors, progesterone receptors and HER2.

To determine one’s subtype of disease, biomarker testing provides specific information about the characteristics of a patient’s tumor. Further, biomarker testing can indicate whether a specific treatment, such as hormone therapy or targeted therapy, is likely to be effective. For example, the presence of specific gene mutations, such as PIK3CA or ESR1 mutations, can also guide the selection of targeted therapies.

Treatment Options for ER-Positive, HER2-Negative Disease

For patients with ER-positive, HER2-negative metastatic, hormone therapy – which blocks the effects of estrogen, thereby inhibiting the growth of cancer cells that rely on estrogen for proliferation – is typically the initial systemic treatment approach. These typically include aromatase inhibitors and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors.

In addition, for premenopausal women, ovarian suppression (which stops the ovaries from producing estrogen) or ovarian ablation (permanent removal of ovarian function) may be used in conjunction with hormone therapy.

If cancer progresses or treatment stops working, the next lines of therapy are considered based on the patient's prior treatments, the presence of new mutations and the overall disease characteristics.

Options in the second-line setting and beyond can include selective estrogen receptor degraders (SERDs), PI3K inhibitors, AKT inhibitors

“There's lots of options in the combination [therapy] space, in the first and second line with oral SERDs and CDKs. There's lots more options for targeted therapies and the PIK3CA space; there's at least four or five other agents and trials that are coming up in that space,” Mardones stated. “[Those agents] came up in the conversation at our meeting too, about their toxicities, which are, unfortunately quite a lot. Although effective agents, they are not conducive to really great quality of life for a long time.”

She concluded her discussion at the CURE® Educated Patient® Metastatic Breast Cancer Updates event by highlighting the need for more oral treatment options for patients.

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