Background: Current guidelines recommend GnRH agonist (GnRHa) use during chemotherapy (CT) as a strategy to reduce the risk of premature ovarian insufficiency (POI) in premenopausal patients with early breast cancer (EBC). However, no long-term safety data are available raising some concerns on concurrent use of GnRHa during CT in patients with hormone receptor-positive disease. In addition, there is no evidence on the protective role of this strategy in patients with germline BRCA mutations (mBRCA). Here, we report the final analysis of the PROMISE-GIM6 phase III randomized study, the largest trial addressing the role of GnRHa use during CT in premenopausal EBC patients (Del Mastro et al, JAMA 2011 & Lambertini et al, JAMA 2015). Methods: From October 2003 to January 2008, 281 premenopausal patients aged 18 to 45 years with stage I-III EBC candidates for (neo)adjuvant CT were randomized to receive CT alone or combined with the GnRHa triptorelin. Primary endpoint was incidence of CT-induced POI (defined as amenorrhea and post-menopausal FSH/estradiol levels 1 year following CT). This final analysis reports on post-treatment pregnancies, disease-free survival (DFS) and overall survival (OS). An exploratory descriptive analysis in mBRCA patients is also reported. (ClinicalTrial.gov: NCT00311636) Results: Of the 281 randomized patients (CT+GnRHa arm = 148; CT alone arm = 133), 80% had hormone receptor-positive disease. At the time of this final analysis, 38 (13.5%) patients were lost to follow-up. Median follow-up was 12.4 years (IQR: 11.3-13.2 years). In the CT+GnRHa and CT alone arms, respectively, 9 (10-year cumulative incidence of pregnancy 6.5%, 95% CI 3.5%-12.3%) and 4 (10-year cumulative incidence of pregnancy 3.2%, 95% CI 1.2%-8.3%) patients had a post-treatment pregnancy (HR 2.14, 95% CI 0.66-6.92). No differences in 10-year DFS (72.4% in CT+GnRHa arm vs. 71.2% in CT alone arm: HR 1.16, 95% CI 0.76-1.77) nor in 10-year OS (82.0% in CT+GnRHa arm vs. 85.9% in CT alone arm: HR 1.17, 95% CI 0.67-2.03) were observed. There was no interaction between treatment effect and hormone receptor status. In patients with hormone receptor-positive disease, HR was 1.02 (95% CI 0.63-1.63) for DFS and 1.12 (95% CI 0.59-2.11) for OS. Out of 43 patients tested for BRCA, overall incidence of POI, irrespective of treatment arm, was 20% in mBRCA patients (n = 10) and 12% in patients without mBRCA (n = 33). In mBRCA patients, incidence of POI was 0% and 33% in the CT+GnRHa and CT alone arms, respectively. One post-treatment pregnancy was described in a patient with mBRCA1 in the CT alone arm. Conclusions: The final analysis of the PROMISE-GIM6 trial at a median follow-up of 12.4 years provides reassuring evidence on the safety of GnRHa use during CT as a strategy to preserve ovarian function in premenopausal patients with hormone receptor-positive EBC. Clinical trial information: NCT00311636