ESR1 and breast cancer: In the present study, we investigated the Cdx2 polymorphism in the vdr gene in a large spectrum of ER-positive (MCF7 and T-47D) and ER-negative (MDA-MB-231, SUM 159PT, SK-BR-3, BT549, MDA-MB-468, HCC1143, BT20 and HCC1954) human breast cancer cell lines.