Adherence to adjuvant endocrine therapy in postmenopausal women with breast cancer

Background: The level of adherence of various pharmacological therapies in chronic diseases varies, but is predominantly low. With tamoxifen (TAM), 23% and 50% nonadherence after 1 and 4 years have been reported. Day-to-day clinical observation suggests that adherence may even be lower with aromatase inhibitors, but limited data exist on the situation in daily clinical routine. The aim of this study was to evaluate the rate of adherent patients in a randomly selected sample of postmenopausal women with primary breast cancer, who had been assigned to an adjuvant endocrine treatment with TAM or anastrozole (ANA). Materials and methods: We investigated a random sample of 100 postmenopausal women with breast cancer (50 TAM and 50 ANA) who had received surgery for their primary breast cancer at our hospital in 2004/2005 and thereafter had been assigned to an adjuvant endocrine treatment. We evaluated the adherence rate with a detailed questionnaire and additionally carried out a retrospective prescription check of the hospital chart as well as calling the local physicians of our patients. A patient was counted as adherent with a self-reported tablet intake of 80% or more and if a medication possession ratio of 80% or more was achieved. Results: Regarding the baseline characteristics, a significant difference in mean age was noticed in women on ANA versus TAM [65 (+/- 3) and 72 (+/- 3); P < 0.001]. All women on TAM and ANA reported to be adherent (100%). After controlling for prescriptions, only 40 (80%) and 27 (69%) of the women on TAM and ANA were still classified as adherent (P < 0.01 and P < 0.01 versus self-report). We found no significant correlation of adherence to any baseline characteristics or side-effects in a logistic regression model. Conclusions: An important goal of any therapeutic intervention is to achieve comparable efficacy in routine clinical practice to that demonstrated in randomised clinical trials. However, a similar magnitude of adherence will be necessary in routine clinical practice to assure comparable clinical effects. Our results further support the data on suboptimal adherence of women with breast cancer on adjuvant TAM treatment. Here, we evaluated for the first time the patient reported and real-world adherence on adjuvant ANA and were able to show a similarly low adherence compared with TAM. More prospective studies are needed to increase our understanding of the underlying reasons for nonadherence in women with breast cancer.