DKK1 and breast cancer: Using our panel of endocrine therapy-resistant breast cancer cell lines generated by long-term estrogen-deprived culture conditions, or anti-estrogen treatment (3, 4, 8–11, 18, 27), we examined the gene expression pattern of SOX2, together with the WNT effector genes DKK1 and AXIN2, to assess long-term expression changes of these stem cell markers.