ERBB2 and breast cancer: Neoadjuvant and adjuvant therapies have improved patient outcomes, particularly in metastatic disease.[3] However, approximately 45% to 55% of patients exhibit low HER2 expression, defined as immunohistochemistry (IHC) 1+ or IHC 2+ without amplifying the HER2 gene in fluorescence in situ hybridization (FISH).[4,5] According to the current guidelines for HER2 validation,[6] these patients were classified as HER2-negative BC.