Abstract PO4-01-13: Effect of interruption or discontinuation of endocrine therapy on the prognosis of breast cancer patients: a cohort study using the real-world database
Authors: Huang Ya , Chen Jie , Wu Yunhao 
Published: May 2024

Abstract
Background:Adjuvant endocrine therapy is the most important treatment modality as long as one, which can reduce the mortality risk and the recurrence risk for patients with hormone receptor-positive breast cancer. Currently, few studies has reported the association in poor adherence with overall survival(OS) or disease-free-survival(DFS). However, the use of prescription coverage in previous studies to describe patient adherence to endocrine therapy may not be representative of the patient's actual medication. Additionally, previous studies did not distinguish between interruption and discontinuation of endocrine therapy, which is different to clinician. This research used rigorous follow-up data and aims on the effects of discontinuation and interruption on patients with early-stage hormone receptor-positive breast cancer.
Methods: Based on the Breast Cancer Information Management System (BCIMS), we identified patients diagnosed with stage I-III breast cancer with hormone receptor-positive and received endocrine therapy during January 1, 1990 to January 1, 2018 in West China Hospital (WCH), Sichuan University, China. Briefly, all patients diagnosed with breast cancer were included and prospectively followed from the diagnosis at WCH or the first visit to WCH for breast cancer. Information, including demographic characteristics, medical history, laboratory results, pathological information, treatments and clinical outcomes, were obtained from clinical records and interviews. Kaplan-Meier analysis, Time-Dependent Cox Regression Model, and subgroup analysis were performed to evaluate the effectiveness of interruption or discontinuation of endocrine therapy. And “X-tile” software is used to select cutoff values in survivorship data.
Results:A total of 3,418 eligible patients were included with 8.13(±1.96) years median follow-up. Of these patients, 19.5% did not adhere to standard endocrine regimens, with 6.9% discontinuing and 12.7% discontinuing. The multivariate cox analysis indicates that discontinuation group (DFS:HR=9.71, [95%CI]5.21-18.34,P &lt;0.001; OS:HR=10.41, [95%CI]5.63-19.24,P &lt;0.001) increased the risk of death and breast cancer events compared to the adherence group, but not shown statistical significance difference in the interruption (DFS:HR=1.03,[95%CI]0.23-4.66, P =0.975; OS:HR=1.17, [95%CI]0.26-5.28,P =0.840). We further analyzed the interruption and discontinuation group respectively. In the interruption group, we found cutoff value with 30 months in survival risks but didn't find statistical significance difference in DFS and OS compared to the adherence groups. For the discontinuation group, we divided the patients into low-risk and high-risk groups according to cutoff value (23 months), the final results showed that the high-risk group who took the endocrine therapy less than 23 months had increased the rate of OS(HR=23.98,[95%CI]11.71-49.14, P&lt; 0.001) and DFS(HR=24.03,[95%CI]11.51-50.18, P&lt; 0.001).
Conclusion:This study found that interruption of endocrine therapy may not affect prognosis of HR+ breast cancer patients, but prolonged discontinuation increases the risk of relapse and death. Therefore, clinicians should educate patients taking endocrine therapy and encourage those who discontinue the drug to take the drug again as soon as possible.
A.Kaplan-Meier Curve for OS

B.A.Kaplan-Meier Curve for DFS
Kaplan-Meier Curve for OS and DFS in the Interruption Group according to the events location

Kaplan-Meier Curve for OS and DFS in the Discontinuation Group according to the total duration of medication

Citation Format: Ya Huang, Jie Chen, Yunhao Wu. Effect of interruption or discontinuation of endocrine therapy on the prognosis of breast cancer patients: a cohort study using the real-world database [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-01-13.