Several lines of evidence showed that DACH1 may represent a novel tumor repressor [13, 15], which inhibited growth and metastasis of breast cancer in vivo via blocking Wnt [15]; transforming growth factor-beta (TGF-β) [16], cyclin D1 [17], and estrogen receptor-alpha (ER-α) [18] signaling; and interfering breast tumor stem cell function [19]. This evidence concerns the gene ESR1 and breast cancer.