BRCA1 and breast cancer: For this study, we used primary mammary tumor cell lines derived from a well-characterized GEMM for BRCA1-deficient breast cancer (K14Cre;Brca−/−;p53−/−) and from two different GEMMs for BRCA1-proficient breast cancer (K14Cre;p53−/− and K14Cre;Cdh1−/−;p53−/−).