In breast cancer, mixed results have been reported regarding the specific ALDH1A isoenzyme involved in tumorigenesis and the ALDEFLUORTM assay, with some groups reporting ALDH1A1 as the main enzyme involved and others showing that ALDH1A3 is the accountable isoform [9, 10, 61, 62]. This evidence concerns the gene ALDH1A1 and breast cancer.