ALDH1A1 and breast cancer: In breast cancer, high expression of a cluster of differentiation 44 (CD44) and low expression of a cluster of differentiation 24 or CD24 (CD44positive/CD24negative/low) contribute to cell proliferation and tumorigenesis, while high expression of aldehyde dehydrogenase or ALDH1 is a strong indicator of metastasis [3,4].