In contrast, mutations and CN alterations affecting cell cycle regulators, such as MYCN, CDK4 and CDKN2A/B, except for MDM2, were particularly enriched in the A1/A2 clusters compared with the E1/E2 clusters (P=0.016), suggesting that these genes may have driver roles in A1/A2 tumours. This evidence concerns the gene MDM2 and neoplasm.