ERBB2 and breast cancer: Interestingly, HER2+ and HR+/HER2− BCBM specimens, which are generated from the late and differentiated luminal progenitor mammary cells, respectively, were included in a common cluster, while HR−/HER2− BCBM specimens, which commonly present gene expression profiles similar to mammary myoepithelial (basal layer) cells, were included in a separate cluster, indicating the relationship between the DNAm landscapes and the cell type of origin33,34, as well as supporting the concept that basal-like breast cancer represents a unique disease entity35.