After two weeks, MDA-MB-231 cells transfected with the control siRNA could generate tumors, while MDA-MB-231 cells transfected with CD44 siRNA or ALDH1 siRNA could not (Fig. 6D), indicating that the suppression of CD44 and ALDH1 both reduced the tumorigenicity of breast cancer cells. This evidence concerns the gene ALDH1A1 and breast carcinoma.