Molecular subtyping of UCB is reminiscent of molecular subtyping of breast cancer, in which the analysis of gene expression patterns over the last 15 years resulted in the discovery of four different subtypes (luminal A, luminal B, ERBB2-overexpression, and basal-like) that have different responses to chemotherapy, endocrine therapy or anti-HER2 therapy. This evidence concerns the gene ERBB2 and breast cancer.