This molecular classification delineated at least four biologically different phenotypes: luminal phenotype (generally, estrogen receptor positive tumours), normal breast-like phenotype and estrogen receptor negative tumours, comprising the subgroups of HER2 (overexpression of ERBB2 oncogene) and basal-like phenotypes (tumours expressing genetic markers that are characteristic of the myoepithelium of the normal mammary gland, such as epidermal growth factor receptor, p63 and basal cytokeratins CK 5/6, CK 14, CK17 [13-15]. The gene discussed is ERBB2; the disease is neoplasm.