BRCA1 and breast cancer: For example, a majority of hereditary breast cancers with BRCA1 mutations display a basal-like phenotype [2,4-7], BRCA1 dysfunction in sporadic basal-like cancers has been reported [8-10], and conditional deletion of BRCA1 and p53 in the mammary gland of mice results in a phenotype reminiscent of human basal-like breast cancer [11,12].