About 15%–20% of breast cancer patients are HER2 positive, characterized by HER2 protein overexpression on an immunohistochemistry assay (IHC 3+ score) or ERBB2 gene amplification on in situ hybridization (ISH) [7], while the remaining are HER2 negative, categorized into Luminal and TNBC subclasses based on hormone receptor (HR) status. The gene discussed is ERBB2; the disease is breast cancer.