Abstract PS5-05-04: Healthcare resource use among women treated with adjuvant endocrine therapy for hormone-receptor positive breast cancer: associations with induced vasomotor symptoms and treatment adherence

Abstract Background: Patients with breast cancer who are non-adherent to adjuvant endocrine therapy have worse clinical outcomes than those who are adherent.1 Side effects of treatment, including induced vasomotor symptoms (iVMS), are a common cause of non-adherence.2 There is a knowledge gap on how iVMS and non-adherence in this population are related to healthcare resource use (HCRU). Methods: In a retrospective cohort study using the Guardian Research Network electronic health record (EHR) US database, we identified women aged 18-70 years treated with adjuvant endocrine therapy following an initial diagnosis of stage 0-III hormone receptor-positive breast cancer from Jan 2016-Jun 2023. Women were stratified into 4 subgroups by adherence to adjuvant endocrine therapy (adherence; ≥80% days covered) and presence of iVMS at the start of follow-up (date of therapy initiation)/distinct follow-up periods. All-cause and breast cancer-related HCRU were identified from EHRs and manual curation of clinical notes. HCRU rates were calculated as events/patient-month. Quasi-Poisson regression models were used to calculate incident rate ratios (IRRs) with 95% CIs for all-cause and breast cancer-related HCRU between iVMS (vs. non-iVMS) and adherent (vs. non-adherent) subgroups, adjusted for confounders. Results: 4459 women were included; mean age at index date was 57 years. Most had ≥1 HCRU event during follow-up (99% for all-cause events, 94% for breast cancer-related events); the most common, respectively, were outpatient visits (98% & 93%), laboratory services (88% & 76%), and primary care visits (66% & 62%). As shown in the Table, non-adherent women with iVMS had the highest all-cause and breast cancer-related HCRU rates from 1 to <3 months’ follow-up (7.24 & 3.04 events/patient-month, respectively). Adherent women with iVMS had the highest HCRU rates during follow-up periods thereafter (3 to <12 months, 12 to <36 months, and 36 to 60 months; see the Table). In the regression models, patients with iVMS had higher rates of all-cause and breast cancer-related HCRU vs. those without iVMS over all follow-up periods (IRRs ranged from 1.16-1.30 and from 1.19-1.35, respectively). Irrespective of iVMS, adherent patients had a lower rate of all-cause and breast cancer-related HCRU vs. non-adherent patients in the first 3 months’ follow-up (IRR 0.84, 95% CI: 0.81-0.87 and IRR 0.77, 95% CI: 0.74-0.80, respectively) and higher rates in later follow-up periods (p<0.001). Conclusion: Our results suggest that women who experience iVMS after adjuvant endocrine therapy for hormone receptor-positive breast cancer have higher rates of HCRU than those who do not experience iVMS. Effective management of iVMS could translate into lower HCRU rates. Refs 1. Eliassen et al. BMC Cancer. 2023;23(1):625. 2. Franzoi et al. Lancet Oncol 2021; 22: e303-13 Citation Format: A. Reddy, N. Schoof, M. Sophie, C. Proenca, C. Caetano, C. Seitz, A. Frenz, K. Genga, J. Milosavljevic, S. Hagenaars, C. Flach, J. Nguyen. Healthcare resource use among women treated with adjuvant endocrine therapy for hormone-receptor positive breast cancer: associations with induced vasomotor symptoms and treatment adherence [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-05-04.