MDM2 and sarcoma: The difference in the number of sarcomas that developed in the Mdm2+/−Arf+/−p53+/− mice (9 of 15 mice) compared to the Mdm2+/+Arf+/−p53+/− mice (15 of 16 mice) was statistically significant (p = 0.0247, chi-squared test).