Abstract GS2-04: Improvements in long-term outcome for women with estrogen receptor positive (ER+) early stage breast cancer treated with 5 years of endocrine therapy: Analyses of 82,598 women in the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) database

Abstract

Abstract Background: For women with ER+ early stage breast cancer who are disease-free after 5 years of scheduled endocrine therapy, recurrences occur at a steady rate to at least year 20 from diagnosis, and are strongly correlated with tumor and nodal status (TN). For women diagnosed in 1976-2011, 20-year distant recurrence (DR) risk was 13%, 20%, and 34% for T1N0, T1N1-3, and T1N4-9 disease, respectively (Pan et al NEJM 2017). Using updated data, we investigated whether DR risk is lower for women diagnosed more recently. Methods: Kaplan-Meier and Cox regression analyses, stratified by trial, TN status and treatment, included 82,598 women with ER+ breast cancer from 108 trials who were alive and disease free after 5 years of scheduled endocrine therapy, 19,675 more than in the previously published dataset, of whom 11,391 were diagnosed since 2005. Results: Estimates of DR during the period from 5 to 20 years were 1% to 2% lower in the updated dataset than reported in 2017. Compared to earlier years (before 1995), the hazard ratio (HR) for DR in years 5-9 was 0.83 (95%CI 0.77 - 0.90) in women diagnosed in 1995-99, decreasing to 0.64 (0.59 - 0.70) in 2000-04, and to 0.58 (0.52 - 0.65) in 2005-12. Those diagnosed after 2000 (median follow-up after year 5 = 2.7, IQR 1.1-4.3 years) had a 30% lower risk of DR (HR = 0.70 (95% CI 0.66 - 0.75) compared with women diagnosed before 2000 (median follow-up after year 5 = 6.1, IQR 4.4-9.9 years). The recurrence risk in years 5-10 after diagnosis in women diagnosed after 2000 was 3% for T1N0 and 5% for T2N0, with few events recorded after year 10. If these recurrence rates continue at the same rate, 20-year risk of DR for women diagnosed after 2000 is projected to be 8% and 14% for T1N0 and T2N0 stages, respectively, compared with 13% and 19% for those diagnosed before 2000. More detailed analyses and investigation of factors influencing the improvements in outcome will be presented. Conclusion: The risk of DR at 20 years after diagnosis for women with node-negative ER+ early stage breast cancer, who discontinue endocrine therapy at 5 years is likely to be about a third lower now than in our previous report. However, long-term follow-up of patients diagnosed more recently is required to accurately characterize long-term recurrence risks. Reference: Pan H, Gray R, Braybrooke J, Davies C, Taylor C, McGale P, et al. 20-year risks of breast-Cancer recurrence after stopping endocrine therapy at 5 years. N Engl J Med. 2017;377:1836-46. Citation Format: Hongchao Pan, Jeremy Braybrooke, Richard Gray, Richard Peto, Rosie Bradley, Robert Hills, Jonas Bergh, Sandra M Swain, Mitchell Dowsett, Daniel F Hayes, Richard D Gelber, for the EBCTCG. Improvements in long-term outcome for women with estrogen receptor positive (ER+) early stage breast cancer treated with 5 years of endocrine therapy: Analyses of 82,598 women in the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) database [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr GS2-04.