CD24 and breast cancer: Hennessy et al. reported that in contrast to other breast cancers, most metastasis breast cancers (MBCs), with stem cell–like features of aggressive, chemoresistant, and poor outcomes, displayed a significant similarity to a ‟tumorigenic” signature defined using CD44(+)/CD24(−) breast tumor-initiating stem cell-like cells (Hennessy et al., 2009).