In the meta-analyses conducted by the Early Breast Cancer Trialists’ Collaborative Group (Oxford Overview), patients with ER+ disease significantly benefited from adjuvant endocrine therapy with tamoxifen as well as polychemotherapy with either CMF (cyclophosphamide, methotrexate, and 5-fluorouracil) regimen or anthracycline/taxane-based regimens [3, 34]. This evidence concerns the gene ESR1 and breast cancer.