ESR1 and breast cancer: Since the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) meta-analysis on the relevance of ER expression, the results of several randomized controlled trials (RCT) investigating newer agents (ovarian function suppression [OFS], aromatase inhibitors [AI] and molecularly targeted agents) have matured and have been summarized in further meta-analyses, showing continued, albeit in some cases borderline, improvements over tamoxifen.3