Abstract GS3-03: Effects of prolonging adjuvant aromatase inhibitor therapy beyond five years on recurrence and cause-specific mortality: An EBCTCG meta-analysis of individual patient data from 12 randomised trials including 24,912 women

Effects of prolonging adjuvant aromatase inhibitor therapy beyond five years on recurrence and cause-specific mortality: an EBCTCG meta-analysis of individual patient data from 12 randomised trials including 24,912 women Background: Five years of endocrine therapy with tamoxifen and/or an aromatase inhibitor is highly effective in reducing the risk of recurrence but a substantial risk remains after treatment discontinuation. Continuing treatment with an aromatase inhibitor may mitigate this risk. Methods: We sought individual patient data for meta-analysis from 12 randomised trials that compared 3-5 years of aromatase inhibitor versus no further treatment after five or more years of endocrine therapy. Primary outcomes were recurrence, and breast cancer mortality. Predefined subgroup comparisons were or prior endocrine therapy (tamoxifen alone, tamoxifen then AI, AI alone), site of recurrence (distant, local, contralateral), age, nodal status, tumour size, grade, and period of follow-up (yrs 0-1, 2-5, 5-9, 10+). Five trials randomised 2-3 years prior to treatment divergence and the primary analyses included only women who were recurrence and second primary cancer free and still alive at the point of treatment divergence. Results: Data have so far been received on 7,488 women (100% of those randomised) in trials of extended AI following tamoxifen alone, 10,796 women (82% 0f 13,192 randomised) following prior tamoxifen then AI, and 959 (23% of 4,229 randomised) following AI alone. Preliminary analyses including 1,617 breast cancer recurrences and 854 breast cancer deaths confirm a 35% reduction in recurrence with extended AI following tamoxifen alone but suggest a more moderate reduction after prior AI therapy. Data from two trials (NSABP B-42 & N-SAS BC 05) contributing ˜5666 women should be available before SABCS to allow definitive analyses. Conclusion: This meta-analysis will provide the most reliable possible summary of the available evidence to inform clinicians on the efficacy of extending AI therapy compared to stopping AI after about 5 years of endocrine therapy in preventing disease recurrence and death from breast cancer, both overall and in different categories of women. Citation Format: Gray R, Early Breast Cancer Trialists9 Collaborative Group. Effects of prolonging adjuvant aromatase inhibitor therapy beyond five years on recurrence and cause-specific mortality: An EBCTCG meta-analysis of individual patient data from 12 randomised trials including 24,912 women [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS3-03.