Seminal studies applying microarray-based technology to BC research demonstrated the phenotypic heterogeneity of BC to be accompanied by a parallelized diversity in transcriptomic profiles, and segregated BCs into five primary molecular subtypes—luminal A, luminal B, basal-like (BL), Her2+ and normal breast-like—each with distinct transcriptomic signatures. This evidence concerns the gene ERBB2 and breast cancer.