Patients with triple-negative breast cancer (TNBC), or those individuals with breast cancer cells that do not express estrogen, progesterone, or human epidermal growth factor receptor 2 receptors (ER-/PR-/HER-), may be able to add miR-21 to the list of potential prognostic biomarkers. A study from The American Journal of Pathology, “Stromal Expression of miR-21 Identifies High-Risk Group in Triple-Negative Breast Cancer,” identified altered miR-21 expression profiles in the tumor stroma of patients with TNBC.
“Predictive biomarkers for therapeutic response prediction and novel therapeutic targets that address distinct biological features of TNBC subgroups are needed for these patients,” said Lorenzo F. Sempere, PhD, head of the Laboratory of microRNA Diagnostics and Therapeutics at Van Andrel Research Institute, in a press release from the publishers. “These findings add support to the growing importance of miRNA-based diagnostics.”
Dr. Sempere’s research team previously showed miR-21, a noncoding regulatory RNA that modulates gene expression, is associated with poor outcomes in colon, pancreas, and breast cancers. The team became particularly interested in miR-21’s involvement in TNBC outcomes and looked at the location and level of miR-21 expression.
Going into experiments, the team had an idea that the tumor microenvironment (stromal and immune cells, extracellular matrix, and cytokines or chemokines) may play a larger role in patient outcomes than changes in cancer cells themselves. Tissue from 901 non-metastatic invasive breast cancer patients demonstrated just that.
Over 40% of cases had miR-21 expression in either low or high levels. Twenty of these cases showed expression only in tumor epithelia, and 187 showed expression predominantly in the stroma. Recurrence-free survival and cancer-specific survival were significantly shortened by higher expression of miR-21. These metrics were even worse when patients had high levels of miR-21 in the tumor stroma.
“This knowledge could be exploited to implement tumor compartment-specific anti-miR-21–based therapies in breast cancer, especially in TNBC cases for which effective targeted therapies are still lacking,” said Dr. Sempere. The results can have a significant impact, as 15-20% of breast cancer cases are classified as TNBC.