ALDH1A1 and lung carcinoma: Lung cancer stem cells have previously been reported based on the expression of surface markers, such as CD133, CD44 and CD117 [18,[20], [21], [22], excessive efflux of the DNA-binding dye, Hoechst 33342 [23] and increased aldehyde dehydrogenase 1 (ALDH1) activity [19].