ALDH1A1 and cancer: Interestingly, the NOTCH signaling indirectly activates the enzymatic activity of ALDH1A1, a well-known marker of prostate cancer stem cells (Ginestier et al., 2007; Li et al., 2010; Le Magnen et al., 2013; Zhao et al., 2014), which are thought to be responsible for tumor recurrence, metastasis and cancer related death (Moltzahn and Thalmann, 2013).