Assessing Adherence to Adjuvant Hormone Therapy in Breast Cancer Patients in Routine Clinical Practice

Adjuvant hormone therapy (HT) in patients with hormone receptor-positive breast cancer (BC) increases overall survival (OS). A lack of adherence to adjuvant endocrine therapy is common, 31.0-73.0% of women discontinue endocrine treatment before 5 years. The aim of the study was to assess adherence to HT in routine clinical practice in patients assisted at the Clinical Oncology Department of the Hospital de Clinicas - Universidad de la Republica, Uruguay.

Patients treated with HT for stage 0-III BC between 2017 and 2019 were included. The medication possession (MPR) rate was calculated using pharmacy records, and the Morisky-Green Scale was applied to assess adherence. Adherent patients were those with MPR ≥ 0.80 and who correctly answered the Morisky-Green treatment adherence questionnaire. The association of adherence with polypharmacy, treatment, and patient characteristics was assessed using simple logistic models. The associations between qualitative variables and adherence were assessed using simple logistic regression model or Fisher's exact test. The association between quantitative variables and adherence was assessed using the Student's t-test. The odds ratio (OR) for non-adherence to treatment and its 95% confidence interval were estimated.

Totally, 118 patients were included; 65.2% were treated with aromatase inhibitors (AIs), 36.0% presenting polypharmacy. The adherence rate at the end of 2 years was 81.0 %; and it was associated with age (P = 0.03, OR = 0.96 for non-adherence), with adherent and non-adherent patients having a mean age of 65.0 and 60.3 years, respectively; however, adherence was not associated with polypharmacy, territory of origin, marital status, living alone, level of education, occupation, or stage. The adherence profile was similar for both drugs, but homemakers and retired women showed greater adherence to AI.

Adherence to HT was assessed in real life, with 19.0% of the patients not adhering to the treatment, despite the known benefit for OS, being a well-tolerated treatment, and being provided free of charge. Older patients were associated with being more adherent. The results show the need of the Pharmacy Service and Department of Clinical Oncology Medical Oncology combining efforts to develop coordinated strategies and interventions to increase adherence, given the impact that this may have on patients' OS.