ALDH1A1 and neoplasm: Seeing that ESA+CD44+ tumor cells have high ALDH activity, the frequency of ESA+CD44+ALDH+ cells is increased in tumors from mice treated with CPA, and ALDH1A1 gene expression is elevated in CPA-resistant CoCSC, we therefore sought to determine whether resistance to CPA was mediated by ALDH1 enzyme activity.