ALDH1A1 and breast cancer: Interestingly, while the fractions of the ALDH1-positive cells were comparable between the HS578T-Hyg breast cancer cells, the M13HS-8 tumor hybrids and their ZEB1-KO variants, the ALDH1-positive cells (27.3 ± 4.0%; Figure 7) were highly enriched in the M13HS-2 ZEB1-KO cells.