Overexpression of the HER2/neu protein (immunohistochemistry 3+), amplification of the HER2/neu gene (fluorescence in situ hybridization positive or chromogenic in situ hybridization positive), or both accounts for approximately 20–25% of invasive ductal carcinomas [4], [5], which is associated with aggressive clinical history in breast cancer patients. The gene discussed is ERBB2; the disease is breast cancer.