Systematic review of real-world studies evaluating the impact of medication non-adherence to endocrine therapies on hard clinical endpoints in patients with non-metastatic breast cancer

Breast cancer, one of the most common malignancies, is associated with significant economic and health burden both at the patient and societal level. Although medication non-adherence to endocrine breast cancer therapies is common, so far only limited systematic evidence has been available on its quantitative consequences, as previous systematic reviews focused mainly on factors contributing to medication non-adherence. The objective of this review was to explore the implications of medication non-adherence to endocrine therapies on hard clinical outcomes in breast cancer based on real-world studies. A systematic literature review was conducted on PubMed; empirical evidence on hard clinical endpoints (i.e., survival, disease-free survival, metastasis and recurrence) were extracted from uni- or multivariate statistical analyses from retrospective or prospective cohort studies. Of the 2,360 identified records, 12 studies met the inclusion criteria. Two studies identified significant positive association between medication non-adherence and the risk of distant metastasis, three articles between medication non-adherence and the recurrence of breast cancer, two studies between medication non-adherence- and non-persistence and of worse disease-free survival and eight articles between medication non-adherence and mortality. There was only one study where the positive association between medication adherence and survival did not apply to all subgroups. The strong evidence on the negative health consequences of non-adherence to breast cancer treatments indicates the need for the regular monitoring of medication adherence. Furthermore, explicit inclusion of adherence enhancing interventions into health policy agenda would be warranted to improve medication adherence also at a system level.