Functional inactivation of tumor suppressor p53 and retinoblastoma (Rb) by Tag lead to initiation of mammary hyperplasia around 8 weeks of age in hemizygous female mice in a hormone-independent manner that further develops to mammary intraepithelial neoplasia which resembles human ductal carcinoma in situ (DCIS) by around the 15th week of age22,23. This evidence concerns the gene TP53 and ductal breast carcinoma in situ.