ERBB2 and breast cancer: Chromatin state shifts may be vital to dictate plasticity in HER2+ BC cells because bivalent chromatin, i.e., simultaneous maintenance of both active and repressed marks at promoter regions of developmental genes [127-130], may hold genes in a so-called poised state that, if activated by specific microenvironmental signals, would either allow non-CSC and CSC-like mesenchymal cells to accrue epithelial characteristics, or non-CSC and CSC-like epithelial cells to accrue mesenchymal characteristics.