Medication Adherence and Health-Related Quality of Life in Patients With Breast Cancer Receiving Oral Anticancer Therapy: A Prospective Observational Study

Purpose This study evaluated medication adherence among patients with breast cancer receiving oral systemic anticancer therapy and examined its associations with sociodemographic, clinical, treatment-related, and health-related quality-of-life characteristics. Methods This prospective cross-sectional study included 95 patients receiving aromatase inhibitor-based therapy, tamoxifen-based therapy, or cyclin-dependent kinase 4/6 inhibitor-based combination therapy. Medication adherence and health-related quality of life were assessed using the eight-item Morisky Medication Adherence Scale (MMAS-8) and EORTC QLQ-C30, respectively. MMAS-8 scores of < 6 and ≥ 6 indicated lower and higher adherence. Binary logistic regression was used to identify factors independently associated with higher adherence. Results Overall, 33 patients (34.7%) had lower adherence and 62 (65.3%) had higher adherence. Disease duration was longer in the lower-adherence group (median, 4.0 vs. 3.0 years; p = 0.029). Adherence differed according to treatment intent ( p = 0.013), medication group ( p = 0.048), and alcohol use status ( p = 0.002). Higher adherence was associated with better global health status and physical, emotional, cognitive, and social functioning and with lower fatigue, pain, dyspnoea, insomnia, and financial difficulties. The median QLQ-C30 Summary Score was higher in the higher-adherence group (80.00 vs. 68.89; p < 0.001). In the multivariable analysis of 80 complete cases, each 10-point increase in the Summary Score was associated with higher odds of higher adherence (adjusted odds ratio, 2.389; 95% confidence interval, 1.488–3.837; p < 0.001). Conclusion Better health-related quality of life was independently associated with higher medication adherence. Concurrent assessment of adherence and quality of life may help identify patients requiring further evaluation and supportive care.