CD24 and breast cancer: Accumulating evidence indicates that CD24-/lowCD44+ breast cancer cells, also referred to as “tumorigenic breast cancer cells” [3, 4], “breast cancer stem cells (CSCs)” [5], and “stem-like breast cancer cells” [6], possess stem cell characteristics, display resistance to conventional therapies, and have high tumor-initiating and metastatic ability [3, 4, 7–9].