BRCA1 and breast cancer: Because disruption of Brca1 in whole body of mouse resulted in embryonic lethality17, we have previously generated a conditional mutant mouse model carrying with MMTV-Cre-mediated deletion of the full-length isoform of Brca1 (Brca1Co/Co;MMTV-Cre) in the mammary tissue, and found the mutant mice developed mammary tumors after a long latency, which is accelerated in a p53 heterozygous background (Brca1Co/Co;p53+/-;MMTV-Cre)8.