ALDH1A1 and breast cancer: However, given that previous studies have demonstrated that expression of ALDH1A1 versus ALDH1A3 isozymes have differential correlation with tumor grade, metastasis, and cancer stage in breast cancer patients [27], we wanted to test the hypothesis that directly inhibiting ALDH using the alternative approach of targeted knockdown of ALDH1A1 or ALDH1A3 would also reduce proliferation, adhesion, migration, and colony formation of breast cancer cells.