Cancer stem cells (CSCs) represent a subset of cancer cells of solid mammary tumors that exhibit self-renewal and can express stemness markers such as CD44+/CD24−/low, aldehyde-dehydrogenase (ALDH), octamer-binding transcription factor 4 (OCT4), and EpCAM (epithelial cell adhesion molecule or CD326), among others. This evidence concerns the gene POU5F1 and cancer.