Approximately 25% of Brca1 mutant mice with either Brca1co/co;Wap-Cre or Brca1co/co;MMTV-Cre developed mammary tumors at about 18 months, and the tumorigenesis could be accelerated by impaired function of p53, which suppresses lethality caused by Brca1 deficiency [10, 11]. Here, BRCA1 is linked to breast cancer.