Adding Ovarian Suppression to Tamoxifen for Premenopausal Breast Cancer: A Randomized Phase III Trial

PURPOSE The addition of ovarian function suppression (OFS) for 5 years to tamoxifen (TAM) for treatment of premenopausal patients with breast cancer after completion of chemotherapy has beneficial effects on disease-free survival (DFS). This study evaluated the efficacy of adding 2 years of OFS to TAM in patients with hormone receptor-positive breast cancer who remain in a premenopausal state or resume ovarian function after chemotherapy. PATIENTS AND METHODS We enrolled 1,483 premenopausal women (age <= 45 years) with estrogen receptor-positive breast cancer treated with definitive surgery after completing adjuvant or neoadjuvant chemotherapy. Ovarian function was assessed every 6 months for 2 years since enrollment on the basis of follicular-stimulating hormone levels and vaginal bleeding history. If ovarian function was confirmed to be premenopausal at each visit, the patient was randomly assigned to complete 5 years of TAM alone (TAM-only) group or 5 years of TAM with OFS for 2 years that involved monthly goserelin administration (TAM + OFS) group. DFS was defined from the time of enrollment to the time of the first event. RESULTS A total of 1,293 patients were randomly assigned, and 1,282 patients were eligible for analysis. The estimated 5-year DFS rate was 91.1% in the TAM + OFS group and 87.5% in the TAM-only group (hazard ratio, 0.69; 95% CI, 0.48 to 0.97; P = .033). The estimated 5-year overall survival rate was 99.4% in the TAM + OFS group and 97.8% in the TAM-only group (hazard ratio, 0.31; 95% CI, 0.10 to 0.94; P = .029). CONCLUSION The addition of 2 years of OFS to TAM significantly improved DFS compared with TAM alone in patients who remained premenopausal or resumed ovarian function after chemotherapy. (C) 2019 by American Society of Clinical Oncology