Since the dawn of the 21st century, intensive research in gene expression analysis has led to the identification of different multi-gene signatures and the characterization of four subtypes of breast cancer, luminal A, luminal B, ERBB-B2-overexpressing and basal-like, and their respective clinico-pathological surrogate definitions, based on immunohistochemistry, i.e., luminal A-like, luminal B-like, HER2 positive (non-luminal) and triple negative (ductal) [5,6,7]. Here, ERBB2 is linked to breast cancer.