Among the multiple isoforms of ALDH, ALDH1A1 and ALDH1A3 are known to be associated with cancer stem cells (112, 113). Interestingly, PRL treatment of HER2-E breast cancer cells was found to suppress the expression levels of both ALDH1A1 and ALDH1A3 mRNA expression. This evidence concerns the gene ERBB2 and breast cancer.