Marcato et al. [28] reported that an increased ALDH activity in breast cancer stem cells is due to the effects of the isoform ALDH1A3, while Chen et al. [29] reported that ALDH1B1 is more profoundly expressed in adenocarcinomas than ALDH1A1, although the function and the cellular localization of ALDH1L2 remain unknown. Here, ALDH1A1 is linked to breast cancer.