ERBB2 and breast cancer: On the basis of the latest guidelines of the American Society of Clinical Oncology (ASCO)/American College of Pathologists (CAP) for the HER2 detection method and scoring system (8), the HER2-low BC was defined as HER2 immunohistochemistry (IHC) 1+/2+ and fluorescence in situ hybridization (FISH) negative (9, 10).