Abstract
PURPOSE: Adherence to adjuvant hormone therapy (AHT) is critical for improving survival in breast cancer patients. This study examines how socioeconomic disparities, osteoarthritis (OA), and OA symptom onset timing influence AHT adherence and survival outcomes. PATIENTS AND METHODS: This retrospective cohort study included 33,142 women with invasive breast cancer (2011-2015) from the Korean National Health Insurance Service. Group-based trajectory modeling (GBTM) identified AHT adherence patterns based on the proportion of days covered (PDC) over five years. Competing risk regression and Cox models assessed the impact of socioeconomic factors, pre-treatment OA, NSAID use, and other variables on AHT discontinuation and survival. RESULTS: GBTM revealed two adherence patterns: high adherence (83.4 %) and low adherence (16.6 %), with the latter showing a rapid decline in PDC. The low adherence group had a significantly higher risk of treatment discontinuation (SHR: 14.06; 95 % CI: 12.50-14.96; p < 0.001) and mortality (HR: 3.56; 95 % CI: 3.09-4.09; p < 0.001). A longer OA history before AHT (p = 0.001) and pre-AHT NSAID use (p < 0.001) were linked to higher discontinuation risk. Patients with Medical Aid/Veteran insurance (OR: 0.60; 95 % CI: 0.53-0.67; p < 0.001) and those in non-capital regions (OR: 0.74; 95 % CI: 0.69-0.79; p < 0.001) were less likely to show high adherence. CONCLUSION: AHT adherence is influenced by socioeconomic factors, pre-existing OA, and OA symptom timing, affecting survival outcomes. Tailored interventions are needed to improve AHT adherence and survival.