Afterwards, isolation of CSCs in ovarian cancer has been explored in various ways, including side population (SP) cells with expression of adenosine triphosphate (ATP)-binding cassette (ABC) transporters, the use of cell surface markers, and detection of aldehyde dehydrogenase activity (ALDH) by using the ALDEFLUOR fluorescence assisted cell sorting (FACS) method. The gene discussed is ABCG2; the disease is ovarian carcinoma.