Poorly differentiated human breast cancers tend to express an “embryonic stem cell-like” signature that contains activation targets of Nanog, Oct4, Sox2, and c-Myc (5), and it has been demonstrated in the MCF-7 breast cancer cell line that Sox2 up-regulates 145 genes, and down-regulates 41 genes (6). This evidence concerns the gene POU5F1 and breast cancer.