Experiments with cancer rat model using NMU (N‐nitroso‐N‐metilurea) as carcinogen had shown that 9‐cis‐isomer of retinoic acid (9cRA) is effective for preventing mammary cancer and enhances the chemopreventive activity of low doses of tamoxifen, increasing expression of E‐ cadherine, at cell–cell contact sites in BC cells. This evidence concerns the gene CDH1 and breast cancer.