ALDH1A1 and cancer: Zhou and colleagues analyzed the contribution of the 19 ALDH isoforms to the ALDHHigh cell compartment in cancer cell lines and found 9 of these to be detected by the ALDEFLUOR assay.35 The ALDH1 subfamily is prominently associated with stem cell properties and drug resistance in cancer.22,27,29,36-39 ALDH1 enzymes are required for the biosynthesis of retinoic acid (RA) in the cytosol.