The mRNA level of KLF4 from all 683 samples was also correlated with that of ALDH1A3 (R = 0.0915, P = 0.0168), but not CD44 or CD24. We further analyzed microarray dataset GSE52262 and GSE52327 [4] and found that the mRNA level of SIRT1 was decreased but that of KLF4 was elevated in ALDH1+ population isolated from human breast cancers (Fig. 2f). This evidence concerns the gene SIRT1 and breast cancer.