BC can be categorized into four subtypes based on the expression of these biomarkers: luminal A (ER/PR+, HER2−, Ki67−), luminal B (ER/PR+, HER2+, Ki67+), HER2-overexpressed (HER2+), and triple-negative breast cancer (TNBC) (ER−, PR−, HER2−) [2]. The gene discussed is ERBB2; the disease is breast cancer.