BC is a very heterogeneous disease and based on gene expression profiling as well as immunohistochemistry it can be classified into five major molecular subtypes, Luminal A and Luminal B subtypes that express estrogen and progesterone receptors (ER and PR), HER2 overexpressing (HER2+) subtype which is characterized by the overexpression of the HER2 receptor, Triple Negative (TN) subtype that lacks expression of ER, PR and HER2 and normal-like that is ER and PR positive and HER2 negative (3). The gene discussed is ERBB2; the disease is breast cancer.