Factors Associated with Intentional Non-adherence to Endocrine Treatment Among Early Breast Cancer Survivors: A Multicenter Cross-Sectional Study

Purpose Adherence to adjuvant endocrine therapy (AET) is crucial for reducing recurrence and mortality in early hormone-receptor-positive breast cancer (BC) survivors, yet it remains suboptimal. This study examined adherence to AET and identified associated factors to inform targeted support strategies. Methods A multi-centre, cross-sectional study included 920 BC survivors (median age 53 years) undergoing AET. Adherence was measured using the Medication Adherence Report Scale (MARS-5), while quality of life (QoL) and adverse effects (AE) were assessed using the Functional Assessment of Cancer Therapy-Endocrine Subscale (FACT-ES). Results Self-reported adherence during implementation phase was 51%. Among non-adherent patients, 71% were unintentionally and 29% intentionally non-adherent. Of 329 patients who missed doses in the prior month, only 2.4% missed more than 20% of prescribed doses. Poorer QoL (p = 0.009), greater AE burden (p = 0.007), younger age (p < 0.001), and tamoxifen treatment (p = 0.01) were factors linked to intentional non-adherence. Intentional non-adherence increased the odds of missing more doses (p < 0.001) and discontinuing treatment (p = 0.001). AET discontinuation occurred in 1.5% of patients, while 17% considered stopping the treatment, with endocrine AE as the primary reason for both. Conclusion Although half of the patients reported not fully adhering to AET, only a small fraction missed enough doses to compromise treatment conduction. Implications for Cancer Survivors Distinguishing between subtypes of non-adherence and identifying modifiable factors such as AE and QoL issues, interventions can be tailored to meet the specific needs of patients, especially those at higher risk of non-adherence.