ALDH1A1 and ovarian cancer: Ovarian cancer stem cells are widely researched using established markers such as aldehyde dehydrogenase (ALDH1) [6–10] or leucine-rich, repeat-containing G protein-coupled receptor 5 (LGR5) [11–15], mostly in ovarian cancer cell lines (e.g., OVCAR3, SKOV3, IGROV1) in vitro.