TP53 and neoplasm: Moreover, both Eμ-Myc/Mdm2+/+ and Eμ-Myc/Mdm2C305F/C305F mice showed induced levels of p19ARF in tumor-bearing mice compared to non-tumor-bearing littermates, suggesting that p19ARF-Mdm2-p53 signaling remains intact in the Mdm2C305F/C305F mice.