siRNA was used to knockdown expression of two ALDH1 isozymes (ALDH1A1 and ALDH1A3) in MDA-MB-468 and SUM159 breast cancer cells and generate the following cell populations: 468CON, 468ALDH1A1low, 468ALDH1A3low, 159CON, 159ALDH1A1low, and 159ALDH1A3low. This evidence concerns the gene ALDH1A3 and breast cancer.