Since in breast and ovary cancers, two main populations of cancer stem cells (CSCs) have been characterized according to the expression of CD44+/CD24− (mesenchymal-like CSC) or ALDH+ (epithelial-like CSC) [39,40,41], both endowed with tumor-initiating potential, we tested OV7 and OVCAR3 for expression of CD117 (c-kit), CD44, CD24 and for the enzymatic activity of aldehyde dehydrogenase 1 (ALDH1) (Figure 3A–D). The gene discussed is ALDH1A1; the disease is cancer.