ALDH1 and cancer stem cell (CSC) markers are expressed in different cell populations in malignant ovarian tumors. [A-B] shows ALDH1 (brown) and CD44 (black) immunostaining in different cells in the tumor stroma. Representative image showing CD44+ cells (presumptively blood cells) primarily localized in or near blood vessels (dotted line). [C-D] shows localization of ALDH1 (brown) and CD117 (black) immunostaining in different cells. CD117+ cells were exclusively localized in the tumor epithelium. [E-F] shows ALDH1 (brown) and CD133 (black) immunostaining in different cells. CD133+ cells were localized to the tumor apical surface of epithelial cells in discontinuous patches of stained (solid arrows) and adjacent unstained cells (dotted arrows). Sections were not counterstained. (Original magnifications: ×200, ×400, ×200, ×400, ×200 and ×400 respectively).