We previously found that heterozygous germline deletion of Brca1 (Brca1+/-) or mammary epithelia specific deletion of Brca1 (Brca1MGKO) in p18-deficient mice eliminated the expression of Gata3 in tumor-free mammary tissue and mammary epithelial cells (MECs) 7, 20. Here, BRCA1 is linked to neoplasm.