Abstract P3-12-04: Extending therapy after 5-year adjuvant hormone therapy in breast cancer patients: A population-based study

Abstract

Background: Clinical guidelines have recommended breast cancer patients with certain characteristics to extend their therapy after 5-year adjuvant hormone therapy. However, no study thus far has described the prevalence, predictors, and outcomes of extending adjuvant hormone therapy in the real world. Methods: We identified 2,937 breast cancer patients who completed 5-year adjuvant hormone therapy during 2010-2019 in Stockholm, Sweden, by linking the Quality Register for Breast Cancer, Prescribed Drug Register, and Cause-of-death Register. We followed them until September 2020. Extended adjuvant hormone therapy was defined as having at least 2 prescriptions of tamoxifen and/or aromatase inhibitors after completing 5-year therapy. We used logistic regression to examine predictors of extended adjuvant hormone therapy and Cox regression to examine whether extended therapy is associated with distant metastasis-free survival, disease-free survival and all-cause mortality. Results: The proportion of extending therapy after 5-year adjuvant hormone therapy increased by 7 times during the past decade, from 8.8% in 2010 to 63.7% in 2019. Predictors of extended adjuvant hormone therapy included young age (≤50 years) at extension, positive lymph node status, high tumor grade and chemotherapy, among which chemotherapy was the strongest predictors [adjusted hazard ratio (HR), 4.64 (95% CI, 3.64-5.92)]. Among patients with chemotherapy, extended therapy improved distant metastasis-free survival [adjusted HR, 0.34 (95 CI%, 0.15-0.78)] and disease-free survival [adjusted HR, 0.61 (95 CI%, 0.39-0.95)]. Therapy discontinuation rates were similar during the first and second five years. Conclusion: Increasing number of breast cancer patients are extending adjuvant hormone therapy, even among patients without clear recommendations in clinical guidelines. Our findings support extended adjuvant hormone therapy in breast cancer patients with chemotherapy. Citation Format: Erwei Zeng, Wei He, Jenny Bergqvist, Kamila Czence. Extending therapy after 5-year adjuvant hormone therapy in breast cancer patients: A population-based study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-04.