Approximately 10–20% of breast carcinomas that are initially classified as HER2-equivocal through IHC are later found to be HER2-amplified using fluorescence in situ hybridization (FISH) testing, ensuring that patients who would benefit from HER2-targeted therapies, such as trastuzumab or pertuzumab, receive the appropriate treatment [6]. The gene discussed is ERBB2; the disease is breast carcinoma.