Understanding Estrogen Receptor-Positive Metastatic Breast Cancer

It is key for patients to understand what estrogen receptor (ER)-positive breast cancer is and how this understanding can help make treatment decisions moving forward, according to Dr. Patrick I. Borgen.

Discovered in the 1960s, a famous researcher found that breast cancer cells make a protein that is a receptor for estrogen — and this protein is not on the surface of the cell, but in the nucleus of it, said Borgen – who is the chair of surgery and director of the Breast Cancer Program at Maimonides Breast Center in Brooklyn, New York.

“(This means) that any estrogen in the body can go through the cell through the cytoplasm into the nucleus and bind to this receptor,” he explained during a breakout session at Susan G. Komen Greater New York City’s New York Metastatic Breast Cancer Conference. “And when it binds, it presses on the gas pedal and the cells are accelerating.”

Breast cancer cells may be either ER-positive and/or progesterone receptor-positive — and knowing this status can be helpful in determining treatment options. Keeping these receptors from attaching to the hormones can help keep the cancer from growing and spreading and, like other cancer types, certain drugs can be used to do this.

For example, hormone therapy drugs can be used to other lower estrogen levels or to stop the hormone from being activated on breast cancer cells. Meanwhile, in the last decade, researchers realized chemotherapy may not be the best treatment option for those with ER-positive disease.

“In a huge subset of breast cancers, maybe more than half (of cases), blocking estrogen can be as potent, or even more potent, than cytotoxic chemotherapy,” Borgen said, adding that a 21-gene expression panel called Oncotype DX has played a major role in genomic profiling of breast cancer.

“The science of the genomic assay has taught us that there's a subset of women who we are wasting our time giving chemotherapy to, and it's dangerous, it's expensive and quality of life is terrible.”

Borgen also noted that there are key differences between genomic and genetic testing that patients should be aware of. “Genetics is what we’re born with. Genomics in simplest terms, is what our genes are saying,” he explained.

In addition to understanding one’s cancer risk to inform family members, genetic testing among patients diagnosed with breast cancer is also key in determining treatment options.

“There are treatments now, specifically for BRCA mutation carriers in the (metastatic breast cancer) setting, that work,” Borgen said. “We do a poor job of identifying families that have these mutations. In fact, the current national guidelines miss 50% of families that have BRCA1 and BRCA2 mutations. We have effective therapies now in subsets of patients with (metastatic breast cancer) that the target the BRCA mutation. So, as a policy we should test newly-diagnosed patients with metastatic breast cancer.”