Adding ovarian function suppression to tamoxifen in young women with hormone-sensitive breast cancer who remain premenopausal or resume menstruation after chemotherapy: 8-year follow-up of the randomized ASTRRA trial.

506 Background: Addition of Ovarian Suppression to Tamoxifen in Young Women With Hormone-Sensitive Breast Cancer Who Remain Premenopausal or Regain Vaginal Bleeding After Chemotherapy (ASTRRA) trial, at 63 months median follow-up, showed that the addition of 2 years of ovarian function suppression (OFS) to Tamoxifen (TAM) significantly improved disease-free survival (DFS) compared with TAM alone in patients with hormone receptor–positive breast cancer who remain in a premenopausal state or resume ovarian function after chemotherapy. We report updated long-term outcomes from ASTRRA trial with 106.4 months median follow-up. Methods: This study is a post-trial follow-up of the ASTRRA trial, which randomly assigned 1,298 patients with breast cancer in a 1:1 ratio to receive TAM only (n = 647) or TAM + OFS (n = 635). The primary endpoint was DFS and secondary endpoint was overall survival (OS). We used Kaplan-Meier estimates for time to event endpoints and hazard ratios (HR) with 95% confidence interval (CI) from Cox-regression model. Results: At 106.4 months of median follow-up, there continues to be a statistically significant reduction in DFS event rate in favor of the TAM+OFS group. The estimated 8-year DFS rate was 85.4% in the TAM + OFS group and 80.2% in the TAM-only group (HR 0.67; 95% CI, 0.51 to 0.87). There were no significant differences in OS between two groups. The estimated 8-year OS rate was 96.5% in the TAM + OFS group and 95.3% in the TAM-only group (HR, 0.78; 95% CI, 0.49 to 1.25). The results of DFS and OS between the two groups defined from the time of random assignment to the time of events were also similar. Conclusions: These data demonstrate consistent survival advantages of adding OFS 2 years to TAM treatment over time, with the long-term follow-up reported to date. This study finding suggest that adding OFS to TAM should be considered for those who remain in a premenopausal state or resume ovarian function after chemotherapy. Longer follow-up is needed to fully evaluate the OS benefit.