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. The gene discussed is ALDH1A1; the disease is breast cancer.