Adherence to hormonal therapy in breast cancer patients: EHR-based retrospective data analysis

Adherence to adjuvant endocrine therapy (AET) is critical for hormone receptor-positive breast cancer but declines over time. We analyzed 6,019 patients from the Asan Biomedical Research Environment (ABLE) who completed five years of anti-estrogen therapy after surgery (2010–2018). Medication adherence, measured by the Medication Possession Ratio (MPR), decreased from 97% to 66%, with especially sharp declines during years 1–2 and 4–5. Poor adherence was associated with age ≥50, aromatase inhibitors (AIs) monotherapy, and absence of radiation therapy (p<0.001). Patients switching from selective estrogen receptor modulators (SERMs) to AIs showed the highest adherence. These findings highlight the need for early identification of patients at risk and the development of tailored clinical management strategies. Digital health interventions may offer support but require further validation in clinical settings.