As a marker of stem cells in both normal tissues and cancers [41], ALDH1 plays an extremely important role in ovarian cancer stem cells [25, 42] because studies show that ALDH1 activity is directly related to a subpopulation of ovarian cancer cells with cancer stem cell-like properties [36, 37, 39, 43–45]. The gene discussed is ALDH1A1; the disease is cancer.