There was a similar tumor spectrum in Mdm2+/−Arf+/+p53−/− and Mdm2+/+Arf+/+p53−/− mice and between Mdm2+/−Arf−/−p53+/− and Mdm2+/+Arf−/−p53+/− mice. This evidence concerns the gene TP53 and neoplasm.