Breast cancer is commonly divided into four types: Luminal A (ER+, PR+, HER2− and low Ki67 expression), Luminal B (ER+, PR+, HER2−/+, high Ki67 or any level expression), HER2 overexpression (ER−, PR−, HER2+), or basal-like. This evidence concerns the gene ERBB2 and breast cancer.