Similarly to BLG-cre;Brca1fl/fl;Trp53+/– mice, BLG-cre;Brca1fl/insC;Trp53+/– mice developed mammary tumors with characteristics of basal-like breast adenocarcinoma (49, 51) with near-absent mRNA expression of estrogen and progesterone receptors, as has been reported before for Brca1-null, Trp53-deficient mammary tumors (Supplemental Figure 9 and data not shown, respectively). The gene discussed is BRCA1; the disease is breast cancer.