In T-47D and BT-474 breast cancer cells, mifepristone and ORG-31710 reduced the number of cells transiting the S phase and increased the abundance of hypo-phosphorylated (inactive) Rb, thus arresting the cells at the G1 phase of the cell cycle in association with an increase in p21cip1 expression and reducing cyclin E/Cdk associated kinase activity (presumably Cdk2) (Musgrove et al. 1997). This evidence concerns the gene CDKN1A and breast cancer.