TP53 and neoplasm: Constant degradation in normal embryos or tissues mediated by the E3-ligase activity of Mdm2 renders p53 protein difficult to be detected,1 whereas Mdm4 mainly inhibits the transcriptional activity of p53.2 Repression of these two inhibitors by stress stimuli is the major posttranslational regulatory mechanism controlling p53 activity and stability.3 Once activated, p53 is able to mediate a plethora of responses including inhibition of cellular proliferation important for tumor suppression.