MDM2 and neoplasm: On the other hand, the p53/Rb1 pathways appeared altered differently among the different tumor types at the gene expression level, with pediatric brain tumors showing high MDM2 expression with high SSV burden and with adult pan-cancers instead showing high expression of CCNE1 and E2F3, though with both sets of tumors showing high CDK4 (Fig. 7f).