ALDH1A1 and neoplasm: There is accumulating evidence that their increased expression selects for tumor cell subpopulations exhibiting stem-like or aggressive tumor cell phenotypes, indicating that the tumorigenic “branch” of the retinoic acid pathway might be co-opted in some tumors and/or that other non RA-dependent functional roles of ALDH1A1 and ALDH1A3 might be involved in tumorigenesis [7, 9, 10, 28].