RESUMEN
PURPOSE: Adjuvant endocrine therapy (AET) for ≥ 5 years is generally recommended for women with hormone receptor-positive breast cancer to reduce cancer recurrence/mortality; however, adherence can be suboptimal. We tested determinants of AET adherence using patient characteristics, treatment pathways, AET initiation timing, and multiple healthcare facility use. An underlying objective was to explore how oncological pathways mirror chronic disease management to monitor adherence and target improvement interventions using administrative datasets. METHODS: Using patient-linked administrative health data from the Italian Lombardy Region, we identified 33.291 surviving patients starting AET in 2010-2016, with two (22.939 patients) or five years (8400 patients) follow-up, using a ≥ 80% prescription refill approach to measure adherence and logistic regression to test determinants of adherence. RESULTS: AET crude adherence falls significantly during follow-up, from 94% at 1 Year to 58% at 5 Years. At 5 Years, patients who were older (>70), prescribed tamoxifen-only (OR 0.69; 95% CI 0.57-0.83; p = 0.0001) vs. aromatase inhibitors-only or therapy switches, treated for depression (OR 0.68; 95% CI 0.60-0.78; p < 0.0001), with surgery performed in high-volume hospitals (OR 0.85; 95% CI 0.75-0.97; p = 0.0116) showed lower adherence. Loyalty, or continued care in the surgical hospital (OR 1.73; 95% CI 1.51-2.00; p < 0.0001), undergoing chemotherapy before AET (OR 2.65; 95% CI 2.02-3.48; p < 0.0001), and earlier AET initiation, positively influenced adherence. CONCLUSIONS: Chronic disease monitoring using administrative data can help oncologists focus efforts to ensure AET adherence. Results suggest addressing mental health, age, disease severity patient perceptions, timely AET initiation and therapy switches, and encouraging continued follow-up in the same hospital or better care coordination with outside follow-up specialists.