Heterozygous Trp53+/− mice develop lymphomas, osteosarcomas, fibrosarcomas, hemangiosarcomas, lung adenocarcinomas, and other tumors, which form lethal tumors in 25% of mice requiring euthanasia as early as 16.5 months in the C57BL/6 background (20). The gene discussed is TP53; the disease is angiosarcoma.