ALDH1A1 and breast cancer: In breast cancer, CSCs are characterized by CD44 expression with absent or low CD24 expression (CD44+CD24-/low) or by increased aldehyde dehydrogenase 1 (ALDH1) enzymatic activity or expression; cells displaying either of these phenotypes on gene expression profiling have been associated with tumorigenesis, invasion, and poor prognosis [7].