Jiang et al demonstrated in 2009 that CSC derived from NSCLC contains a population of the ALDH1-positive cells that may generate tumors recapitulating the heterogeneity of the parental cancer cells.45 In 2010 Sullivan et al46 gained further insights regarding ALDH in 45 NSCLC cell lines and in 11 NSCLC patient tumors, confirming that these ALDH-positive to ALDHhigh cells were associated with the NOTCH signaling pathway and with the well-known characteristics of CSCs.47 For these reasons, ALDH expression has been used for the identification of CSCs in many solid tumors. This evidence concerns the gene ALDH1A1 and cancer.