ALDH1A1 and cancer: Given that ALDH1-positive cells are putative CSCs or CSC-like cells and that side population (SP) cells are also putative CSCs in many different cancer cell lines [37–39], the decrease in the proportion of ALDH1-positive cells (Figure 5C and 5D) and SP cells (Supplementary Figure 1) strongly supports that the combination treatment with 5-aza-dC and IR is effective in eliminating pancreatic CSCs or CSC-like cells.