ERBB2 and breast cancer: Based on the American Society of Clinical Oncology and the College of American Pathologists (ASCO/CAP) guidelines, HER2+ is defined as IHC 3+ (circumferential membrane staining including >10% of cells) or IHC 2+ combined with HER2 amplification by an ISH assay of the invasive component of a BC specimen using single/dual-probe ISH.