MDM2 and neoplasm: The tumour suppressor p53 has a pivotal role in preventing tumourigenesis through the induction of cell-cycle arrest and apoptosis.1TP53 is the most frequently mutated gene in human cancer; however, some tumours still harbour wild-type TP53. 2 In these cases, wild-type TP53 function is usually inhibited by the negative regulator mouse double minute 2 (MDM2, HDM2 in humans).