Estrogen receptor β: putting a positive into triple negative breast cancer?

Abstract ERβ was discovered over 15 years ago, yet the initial expectancy that this protein could have therapeutic use has ebbed, because of the complexity surrounding its function and significance in breast cancer. It has become apparent that its functional role and prognostic significance in breast cancer may depend on a number of factors, such as co-expression with ERα, presence of various isoforms (ERβ1, -2 and -5 in breast cancer), post-transcriptional modifications and cellular location. Interestingly, ERβ1 is often expressed in triple negative breast cancer (TNBC), a more aggressive type of breast cancer with limited treatment options because of the lack of expression of a recognised biological target. Furthermore, clinical data has demonstrated a clear correlation between ERβ1 positivity and improved disease-free and overall survival in those patients treated with tamoxifen. This suggests ERβ1 may be worth considering as a potential therapeutic target, particularly in TNBC.