Association between self-report adherence measures and oestrogen suppression among breast cancer survivors on aromatase inhibitors

Abstract

PurposePoor adherence to oral adjuvant hormonal therapy for breast cancer is a common problem, but little is known about the relationship between self-report adherence measures and hormonal suppression. We evaluated the relationship of three self-report measures of medication adherence and oestrogen among patients on aromatase inhibitors (AIs). Materials and methodsWe recruited 235 women with breast cancer who were prescribed AI therapy. Participants self-reported AI adherence by completing the following: (1) a single item asking whether they took an AI in the last month, (2) a modified Morisky Medication Adherence Scale-8 (MMAS-8) and (3) the Visual Analog Scale (VAS). Serum estrone and estradiol were analysed using organic solvent extraction and Celite column partition chromatography, followed by radioimmunoassay. ResultsTen percent of participants reported they had not taken an AI in the last month and among this group, median estrone (33.2pg/ml [interquartile range (IQR)=22.3]) and estradiol levels (7.2pg/mL [IQR=3.3]) were significantly higher than those in participants who reported AI use (median estrone=11.5pg/mL [IQR=4.9]; median estradiol=3.4pg/mL [IQR=2.1]; p<0.001). This relationship held when controlling for race and AI drug type. ConclusionsA single-item monthly-recall adherence measure for AIs was associated with oestrogen serum levels. This suggests that patient-reported monthly adherence may be a useful measure to identify early non-adherence behaviour and guide interventions to improve patient adherence to hormonal treatment.