The association of adverse drug reactions with medication adherence among patients with breast cancer: A systematic review and meta-analysis.

Abstract

IntroductionThis study aimed to systematically evaluate the association between adverse drug reactions, medication adherence, and outpatient treatment outcomes among women with breast cancer receiving oral anticancer therapies.MethodsA systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and guided by the Joanna Briggs Institute methodology. A comprehensive literature search was performed in PubMed, CINAHL Ultimate, Embase, MEDLINE, and Scopus to identify quantitative observational studies published in English from database inception through June 2026. Eligible studies examined the association between adverse drug reactions and medication adherence and/or outpatient treatment outcomes in female patients with breast cancer receiving oral anticancer therapies. Cohort, case-control, and cross-sectional studies conducted in outpatient settings were included. Two independent reviewers screened studies, extracted data, and assessed methodological quality using Joanna Briggs Institute critical appraisal tools. Meta-analyses were conducted when sufficient clinical and methodological homogeneity was present.ResultsForty studies involving 44,455 women were included; all evaluated oral endocrine therapy. Adverse drug reactions were associated with lower medication adherence, although substantial between-study heterogeneity limited confidence in the magnitude and generalizability of the pooled association. Evidence linking adverse drug reactions with outpatient treatment outcomes, including disease-free survival, was limited and heterogeneous, with no consistent association identified.ConclusionsAdverse drug reactions were associated with medication nonadherence among women receiving oral endocrine therapy. However, the very high heterogeneity of the adherence synthesis and the observational nature of the included studies preclude a precise common-effect or causal interpretation.