ERBB2 and breast cancer: In the context of HER2-nonamplified luminal BC, Duru et al. revealed that a subpopulation of HER2+ CD44high/CD24low BCSCs isolated from radioresistant BC MCF7 cells displayed enhanced ALDH activity, aggressiveness, tumor sphere formation, and in vivo tumorigenesis compared with their counterpart HER2-negative CD44high/CD24low BCSCs [56], still supporting the notion that HER2 is a key BCSC biomarker that identifies a cell subpopulation particularly resistant to conventional anticancer therapies.