ESR1 and breast cancer: In 2008, the Korean Breast Cancer Society Study Group initiated the ASTRRA trial to answer the following questions: (1) whether disease free survival benefits could be achieved with the addition of OFS to standard 5-year tamoxifen treatment after the completion of neoadjuvant or adjuvant chemotherapy in premenopausal young women with estrogen receptor-positive disease, and (2) whether delayed OFS treatment could reduce disease recurrence in patients with recovered ovarian function who experienced chemotherapy-induced amenorrhea and who were treated with standard tamoxifen therapy.