ERBB2 and breast cancer: <i>Background and Objective</i>: The clinical success of novel antibody-drug conjugates has led to the identification of a new subgroup within traditionally HER2-negative breast cancers, termed 'HER2-low.' The aim of this study was to investigate the clinicopathological differences between HER2-low and HER2-negative groups in neoadjuvant-naive primary breast cancer patients, with a specific focus on stromal tumor-infiltrating lymphocyte (sTIL) density.