Abstract PO2-12-04: Suboptimal adherence to adjuvant endocrine therapy (ET) in Brazilian women with early-stage estrogen receptor-positive (ER+) breast cancer

Abstract Background: Adjuvant ET reduces breast cancer recurrence and increases overall survival among patients with early-stage ER+ breast cancer, however a suboptimal number of patients in fact takes oral medicine as prescribed. In Brazil, there is a paucity of data about adherence to adjuvant ET. This study aims to evaluate adherence to adjuvant ET in Brazilian women with early breast cancer and to evaluate clinical and sociodemographic characteristics associated with higher or lower adherence. Methods: Women with history of early-stage ER+ invasive carcinoma of the breast on adjuvant ET for at least 6 months were invited to participate of this study. Adherence was assessed with questionnaire Morisky Medication Adherence Scale (MMAS-8) and high adherence was defined by a MMAS-8 score=8. Demographic and medical information, site of treatment (private versus public), degree of education (completed high school vs not) were reviewed from medical records. Quality of life was assessed using EORTC QLQ C30 and BR-23 forms, sexuality was evaluated with the Female Sex Function Index questionnaire. Additionally, patients were interviewed about return to work. Data collection was done with RedCap software. Qualitative variables were compared between groups using the Chi-square or exact Chi-square test and for quantitative variables the non-parametric Mann-Whitney test was used. Multivariable analysis was performed using Poisson regression. P 0.05 was considered significant. Analyzes were performed in SAS 9.4. Results: From June 2021 to May 2023, a total of 461 women with ER+ early-stage breast cancer from 12 Brazilian institutions were included in this analysis. The mean age was 56.0 years (range 22-93), 47.7% were non-white and 38.7% were premenopausal. A total of 233 women (50.6%) had private insurance and the remaining were treated in public institutions. Median duration of ET use was 2.78 years (range 6 months- 9.61 years). High adherence to adjuvant endocrine therapy was present in 55.7% of patients. Median age of high adherent woman was higher than low adherent (p=0.005). Factors significantly associated with high adherence were no use of ovarian suppression (p=0.0095), use of anti-Her2 therapy (p=0.0462). Furthermore, higher scores for EORTC QLQ-C30 global health status (p=0.017) and in specific domains, including role functioning (p=0.007), emotional functioning (p 0.0001), cognitive functioning (p 0.001), social functioning (p = 0,0005), higher scores for EORTC BR23 body image (p 0.001) and future perspective (p = 0.0198) were also associated with high adherence. Higher EORTC QLQ-C30 cognitive function score was the only variable associated with high adherence (p 0.0001) to ET in multivariate model. Conclusion: Using the MMAS-8, only 55.7% of Brazilian women with stage I-III ER+ breast cancer reported high adherence to endocrine therapy. This suboptimal adherence rate leads to important questions such as the impact on the prognosis of this population Charactheristic with adjusted prevalence ratio for the occurrence of High adherence PR: Prevalence ratio; EORTC: European Organisation for Research and Treatment of Cancer Citation Format: Daniele Assad-Suzuki, Heloísa Resende, Danielle Santos, Fernanda Moura, Sulene Oliveira, Andrea Shimada, Anna Luiza Galvão, Bruno Souza, Amanda Castro, Monalisa Andrade, Yuri Beckedorff, Maria Cristina Magalhães, Cristiano Souza, Carlos Paiva, Daniela Pereira, Angelica Rodrigues, Daniela Rosa, Romualdo Barroso-Sousa. Suboptimal adherence to adjuvant endocrine therapy (ET) in Brazilian women with early-stage estrogen receptor-positive (ER+) breast cancer 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 PO2-12-04.