MDM2 and neoplasm: Intriguingly, while mutp53 specifically accumulates in tumors, but not in normal tissues, in p53R172H/R172H mice, further deletion of E3 ubiquitin ligases for mutp53, such as MDM2 or TRIM21, in p53R172H/R172H mice results in mutp53 accumulation in normal tissues and tumors, an earlier tumor onset, and the reduced lifespan of mice, indicating that mutp53 accumulation is a tumor-specific event and mutp53 accumulation is required for mutp53 GOF in tumorigenesis15,17,54,55.