Primary breast cancers can be divided into four molecular subtypes: luminal A (hormone-receptor-positive, HER2-negative), luminal B (hormone-receptor-positive, HER2-positive), HER2-enriched (hormone-receptor-negative, HER2-positive), and TNBC (hormone-receptor-negative, HER2-negative) breast cancers. This evidence concerns the gene ERBB2 and breast cancer.