The neoadjuvant setting provides a unique opportunity to study the effect of systemic treatments on breast cancer biology and to identify clinically useful prognostic and predictive biomarkers. Discrepancies and inconsistencies in the use of definitions and endpoint assessments in this setting confound the analysis and interpretation of results across clinical trials and hinder research progress. This Review represents a joint effort of the Breast International Group and the National Cancer Institute-sponsored North American Breast Cancer Group to provide clinicians and researchers with a series of standardised definitions and endpoints that could be implemented in future neoadjuvant clinical trials. Definitions of the setting of interest and of survival endpoints are recommended, together with proposals for standard assessment of the response to treatment, use of functional and molecular imaging endpoints, and characterisation and selection of the population to treat. We expect that implementation of these recommendations will improve the conduct, reporting, and effectiveness of clinical trials and fully exploit the clinical and scientific potential of the neoadjuvant setting in breast cancer.
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