ALDH1A1 and ovarian serous adenocarcinoma: The various studies carried out on serous ovarian cancer cells with heterogeneous cell populations (tumor cell lines, primary tumors, tumor xenografts and in vitro tumor-spheres) and with various methodologies claimed that CD144 with or without CD117 [194,195], Hoechst-excluding cells (the “side population”) [196], CD24, Epithelial Cell Adhesion Molecule (EpCAM) [195], CD133 [197,198,199,200] and Aldheyde Dehydrogenase-1A1 (ALDH1A1) [201] (Table 4) expression enrich for serous ovarian cancer tumor-initiating cells.