In breast cancer, ALDH1, ALDH1A1, 1A3, and 3A1 have all been identified and correlated with aggression, progression, or poor survival.13–16 ALDH1A3 has also been identified as the main isoform responsible for ALDEFLUOR activity in breast cancer cells.17 In ovarian cancer, ALDH1A1 overexpression was tumor-type specific. Here, ALDH1A1 is linked to breast cancer.