Independent, External, Blinded Retrospective Validation of an AI-based Prognostic Assay in ER-Positive/HER2-Negative Early Breast Cancer

This retrospective observational study evaluates the prognostic performance of a locked Artificial Intelligence (AI)-based assay in patients with Estrogen Receptor (ER)-positive, Human Epidermal Growth Factor Receptor 2 (HER2)-negative early breast cancer (EBC) from Austrian Breast \& Colorectal Cancer Study Group (ABCSG)-8, with extended follow-up from ABCSG-16 where available. ABCSG will provide digitized hematoxylin and eosin (H\&E) slides and required baseline clinicopathologic variables to Spotlight Medical without outcome data for blinded assay inference. ABCSG will then perform the prespecified statistical analyses linking assay outputs to clinical outcomes.