MDM2 and neuroblastoma: Interestingly, in our recent study of paired neuroblastoma tumors established at diagnosis and relapse which demonstrated a high frequency of p53/MDM2/p14ARF pathway abnormalities in relapsed neuroblastoma, a higher frequency of abnormalities involving MDM2 amplification, and p14ARF inactivation (35%) compared to p53 mutations (15%) was observed.