RB1 and triple-negative breast carcinoma: We made use of a recently described mouse model of triple-negative breast carcinoma in which the Rb, p53 and BRCA1 pathways were inactivated in the mammary epithelium using a transgene encoding a fragment of the SV40 Large T-antigen (T121) to inactivate pRb, along with conditional alleles of p53 and Brca1.