Several markers have been proposed to identify and isolate cancer stem cells including CD133, CD44, CD24, CD90, CD34, CD117, CD20, and aldehyde dehydrogenase (ALDH1) [7, 9], a cytosolic enzyme that is responsible for the oxidation of retinaldehydes to retinoids [10, 11]. The gene discussed is ALDH1A1; the disease is cancer.