ER, PR and HER2 testing in breast cancer

The application of targeted therapies has played important roles in the improvement of breast cancer survival rate during the past two decades. Estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) are well established biomarkers for breast cancer prognosis and for guiding treatment. Emerging data furthers our understanding of the biomarkers and their validity as predictive and prognostic indicators. Breast cancer biomarker testing guidelines have been recently updated. There are still several key challenges in the evaluations of these markers, including pre-analytic standards, tissue selection for testing and re-testing, result interpretations, and tumour heterogeneity. In addition to ER, PR and HER2, newer markers and multigene testings may provide additional information in guiding targeted therapy for breast cancer.