ERBB2 and breast cancer: With the advances of high-throughput gene expression microarrays and next-generation sequencing, multiple molecular subtypes of BC differing by their transcriptional signatures have been identified: Luminal A, Luminal B, Normal-like, HER2-enriched, Claudin Low, and Basal-like/Triple Negative (TNBC) [4,5,6,7,8].