ERBB2 and breast carcinoma: Clinical relevance of HER2-low and HER2-ultralow is reinforced by encouraging efficacy findings in these populations.<h4>Objective</h4>To assess HER2-low and HER2-ultralow scoring performance by pathologists, and compare real-world HER2-low scoring with centralized scoring by trained pathologists.<h4>Methods</h4>Formalin-fixed, paraffin-embedded breast cancer samples stained by the VENTANA anti-HER2/neu (4B5) Rabbit Monoclonal Primary Antibody (Roche) assay were selected to ensure adequate representation across all HER2 IHC scores (N = 500).