Kim HA, Lee JW, Nam SJ, et al. - Researchers investigated whether adding 2 years of ovarian function suppression (OFS) to tamoxifen (TAM) would be an efficacious treatment strategy for patients with hormone receptor–positive breast cancer who remain in a premenopausal state or resume ovarian function following chemotherapy. In this study, the enrolled participants were 1,483 in total and comprised premenopausal women (age ≤ 45 years) with estrogen receptor–positive breast cancer managed with definitive surgery following completion of adjuvant or neoadjuvant chemotherapy. If the ovarian function was verified to be premenopausal at each visit, the experts randomly allocated the patient to complete 5 years of TAM alone (TAM-only) group or 5 years of TAM with OFS for 2 years that included monthly goserelin administration (TAM + OFS) group. In the TAM + OFS group and in the TAM-only group, the 5-year disease-free survival (DFS) rate was estimated to be 91.1% and 87.5%, respectively, and the 5-year overall survival rate was estimated to be 99.4% and 97.8%, respectively. Overall, a significantly improved DFS was achieved with the addition of 2 years of OFS to TAM vs TAM alone in patients who continued to be premenopausal or resumed ovarian function following chemotherapy.