ALDH1A1 and ovarian benign neoplasm: However, the utility of ALDH1 as a marker of CSCs is not clear in some solid tumors, such as ovarian cancer; in fact, gene expression studies have reported that ALDH1A1 expression was up-regulated in normal ovary, benign ovarian tumors, and borderline ovarian carcinomas as compared with high-grade malignant ovarian carcinoma [12–14].