Adherence and Persistence to Adjuvant Hormonal Therapy in Early-Stage Breast Cancer Patients: A Population-Based Retrospective Cohort Study in Israel

Background: Adjuvant hormonal therapy (HT) has been consistently proven to improve multiple outcomes in early breast cancer yet rates of adherence and persistence are variable. Methods: We retrospectively identified women diagnosed with nonmetastatic breast cancer and initiating HT between January 2000 and December 2007 in a large Israeli health provider. Prescription records including the drug name, date of purchase, and the quantity of pills dispensed were collected. We used Cox proportional hazards and binary logistic models to analyze factors associated with early discontinuation (<5 years) and nonadherence (proportion of days covered, PDC <80%) of HT, respectively. Results: A total of 4,178 women with breast cancer were identified with nearly 95% of patients treated with tamoxifen as the initial HT. Over the 5-year follow-up period, early discontinuation was identified in 955 (23%) patients. The mean PDC was 82.9% (SD 0.004). Younger age and low BMI were both associated with an increased risk of early discontinuation and nonadherence. A history of hypertension was associated with a higher likelihood of both outcomes. Conclusion: Adherence and persistence with HT among Israeli breast cancer survivors are comparable to those in international reports. Interventions are necessary to identify and prevent suboptimal HT adherence.