While Wap-Cre mouse model system in which Aurora-A was constitutively overexpressed under CAG-CAT promoter in mammary gland after one cycle of pregnancy developed hyperplasia in p53 wild-type background and precancerous atypical ductal hyperplasia in p53–null background (92, 94), MMTV promoter-driven mouse model was reported to develop mammary tumors in both p53 wild-type and heterozygous background after four to five cycles of pregnancy (93). Here, TP53 is linked to breast cancer.