Breast Cancer Test Result Long Seen As Positive May Hide a Bigger Risk

A recent study conducted by researchers from the Karolinska Institutet in Sweden has revealed that the standard breast cancer classification system may be overlooking crucial distinctions that could significantly influence treatment decisions. Breast cancers are categorized based on how the cancer cells respond to hormones, with hormone receptor (HR) positive breast cancers responding to estrogen or progesterone, and hormone receptor (HR) negative breast cancers not responding to hormones.

The findings suggest that the current classification system, which categorizes breast cancers as either ER positive or ER negative, may not accurately reflect the diverse biological profiles of tumors.

The study, published in The Lancet Regional Health – Europe, analyzed data from over 75,000 women diagnosed with HER2-negative breast cancer between 2007 and 2023 in Sweden. Researchers divided these patients into groups based on the percentage of tumor cells expressing the estrogen receptor, finding that ER expression levels between 10 and 29 percent exhibited survival outcomes and molecular characteristics more similar to ER-negative breast cancers.

Notably, patients with ER expression levels between 10 and 59 percent had poorer survival rates compared to those with strongly ER-positive disease. Furthermore, patients receiving both chemotherapy and endocrine therapy showed improved survival outcomes compared to those treated with endocrine therapy alone in these intermediate ER groups.

The study's lead researcher, Balazs Acs, an associate professor at the department of oncology-pathology, stated that these findings support reporting ER expression as a percentage and considering ER expression as a continuum rather than a simple positive or negative marker. He added that further research is needed to explore how these findings can be translated into clinical practice, emphasizing the importance of understanding the biology of intermediate ER-expressing tumors and identifying additional biomarkers to refine risk stratification and treatment selection.

The researchers plan to investigate the role of progesterone receptor expression and other molecular features in determining personalized treatment approaches for patients with breast cancer.