Aldehyde dehydrogenase (ALDH) family members, especially Aldh1 and Aldh3a1, are not only the markers of normal stem cells but also cancer stem cells and play essential roles in maintaining stem cell functions, including proliferation and resistance to cytotoxic drugs in some cancer types, including prostate cancer [45–47]. The gene discussed is ALDH3A1; the disease is prostate carcinoma.