BRCA2 and breast cancer: This may be the reason that BRCA1 and BRCA2 loss gives rise to a more aggravated DNA damage profile, as >90% of Brca1Δ/Δ;p53Δ/Δ tumors and Brca2Δ/Δ;p53Δ/Δ mammary tumors are carcinomas, compared to half of the p53Δ/Δ mammary tumors, of which the other half are sarcomatoid.