TP53 and breast cancer: To study the contribution of MYC overexpression to BRCA1-associated mammary tumorigenesis, we initially employed the K14Cre;Brca1F/F;Trp53F/F (KB1P) mouse model20, in which epithelium-specific loss of BRCA1 and p53 leads to the formation of mammary tumors and, to a lesser extent, other epithelial tumors including skin tumors.