Abstract P4-03-01: Persistence with adjuvant endocrine therapy in patients with early breast cancer at high risk of recurrence: a US-based real-world study
Authors: Sheffield Kristin M. , Vitko Alexandra S. , Brown Jacqueline 
Published: March 2023

Abstract
Background: Previous studies have highlighted concerns regarding treatment persistence (TP) of patients with early breast cancer (EBC) taking adjuvant endocrine therapy (ET) but these data have not been analyzed based on patient’s risk of recurrence. The aim of this study is to evaluate the TP of patients at high risk of recurrence based on clinicopathologic criteria used in the monarchE trial.
Methods: This observational retrospective cohort study used nationwide Flatiron Health electronic health record (EHR)-derived de-identified database of US patients diagnosed with EBC from Jan 2011 to Sept 2020. Overall, 4028 patients were selected based on the following criteria: adult female or male with diagnosis of HR+, HER2– EBC (stage IA-IIIC) with no evidence of distant metastasis who received surgical resection and adjuvant endocrine therapy. Patients were divided into 2 groups; GroupA: patients with clinicopathologic features suggestive of high risk of recurrence: ≥4 positive(+) axillary lymph nodes (ALN), OR 1-3+ ALN and either Grade3 disease, or tumor size ≥ 5 cm, or Ki-67 ≥ 20%. GroupB: patients with stage IA-IIIC disease who did not meet those high risk criteria. TP (time from start to discontinuation of adjuvant ET) was compared between the 2 groups. Patients who had a gap of &gt;90 days after their last date of ET, as documented in the EHR, were considered to have discontinued ET. Patients whose last ET was ≤90 days from Sept 2020 were censored. Cumulative incidence functions of nonpersistence were estimated, treating recurrences or deaths occurring during ET as competing risks.
Results: While gender and race distributions were similar between groups, patients in GroupA (n=557) were younger and more likely to be premenopausal, have an ECOG PS score of 1 or 2+, and have received mastectomy, radiation and chemotherapy compared to GroupB (n=3471). Estimates of the cumulative incidence functions of nonpersistence were statistically different between the groups (p &lt;.001). The Table shows the cumulative incidence (standard error) of nonpersistence at years 1-5 after initiating ET.
Conclusions: This study suggests that patients at high risk of recurrence have higher ET-TP than those at lower risk. The separation was most pronounced at 5 years. The steep increase in 5-year nonpersistence in lower risk group could be due to a perception of less need to continue ET for longer periods of time in lower risk disease. The greater persistence in patients at high risk is noteworthy, but interventions to improve patient’s TP are still warranted.
Table 1: Cumulative incidence of nonpersistence after initiating ET
Citation Format: Kristin M. Sheffield, Alexandra S. Vitko, Jacqueline Brown. Persistence with adjuvant endocrine therapy in patients with early breast cancer at high risk of recurrence: a US-based real-world study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-03-01.