ESR1 and breast cancer: The International Breast Cancer Study Group IX trial found no survival advantage of cyclophosphamide, methotrexate and 5-fluorouracil followed by tamoxifen, over tamoxifen alone, in 1669 postmenopausal women with ER+ node-negative breast cancer at 13.1 years follow-up (64 vs 66%, p = 0.99) [13].