Based on the immunohistochemistry markers and microarray studies, breast cancer can be further classified into five subgroups: Luminal A, characterized by positive ER or PR and negative HER-2; Luminal B, with positive ER and HER-2 or have high levels of Ki-67; HER-2 overexpressing subtype, displaying negative ER and PR but positive HER-2; Basal-like subtype, with negative ER, PR, and HER-2 but positive cytokeratin 6.5; and Normal breast-like subtype (6-8). The gene discussed is ERBB2; the disease is breast cancer.