CD44 and breast carcinoma: While the CD44+CD24−/low surface marker signature and high ALDH activity have been widely used to identify the putative CSC population since the pioneering studies of Al-Hajj et al. [26] and Ginestier et al. [24], respectively, more recent studies have demonstrated that the CD44+CD24−/low and ALDH+ marker profiles associated with putative breast CSCs identify minimally overlapping, spatiotemporally distinct populations across different breast cancer sub-types [38].