Breast cancer stem-like cells (BrCSCs) are identified with cell surface phenotypes of either CD44+/CD24− or aldehyde dehydrogenase 1 (ALDH1) [7–10], and it is now widely accepted that BrCSCs are functionally essential for tumor formation, progression, and therapy resistance in breast cancer patients [3, 11]. Here, ALDH1A1 is linked to breast cancer.