Based on molecular and histological evidence, breast cancer is classified into four major subtypes: Luminal A (ER+, PR+, HER2−), Luminal B (ER+, PR+ HER2+), HER2 enriched (ER−, PR−, HER2+), and basal-like/triple-negative breast cancer (TNBC) [2, 3]. The gene discussed is ERBB2; the disease is breast cancer.