Impact of Adverse Drug Events on Adherence to Adjuvant Endocrine Therapy in Breast Cancer Patients: A Study in a Provincial Oncology Hospital in Vietnam

Abstract

Adjuvant endocrine therapies used in the treatment of breast cancer may cause multiple adverse drug events (ADEs), which can reduce patients’ quality of life and hinder treatment adherence if not properly managed. A cross-sectional study was conducted at Provincial Oncology Hospital among patients who had been prescribed tamoxifen or aromatase inhibitors (AIs) for at least 3 months. ADEs occurring within the previous 4 weeks were recorded and their severity assessed using a 4-point Likert scale, based on a 21-item symptom questionnaire. Treatment adherence was evaluated using the 12-item Adherence to Refills and Medications Scale (ARMS). Among 243 participants (mean age 54,4 ± 10,1 years; 93.4% postmenopausal; 72.8% stage II disease; 53.1% receiving AIs), with a total of 774 events recorded, 199 patients (81.9%) reported at least one ADE and 63 patients (25.9%) experienced at least one severe ADE. Musculoskeletal adverse events were the most frequently reported (26.2%), followed by vasomotor adverse events such as hot flashes (13.0%). The overall non-adherence rate was 48.6%, primarily due to forgetting or missing medication when being careless. Multivariate analysis showed that the occurrence of ADEs was significantly associated with treatment adherence. Specifically, patients experiencing at least one ADE were significantly less likely to adhere to treatment (OR = 0.015; 95%CI: 0.002–0.116), and adherence decreased as the number of ADEs increased (p < 0.001). These findings highlight the importance of early detection and effective management of ADE, as well as strengthening patient education to improve adherence, thereby contributing to better treatment outcomes and improved quality of life.