MDM2/p53 binding antagonists have been demonstrated to have anti-tumour activity in in vivo xenograft models [6, 8], and their clinical potential for the treatment of p53 wild-type tumour types has been confirmed by initial results from phase I clinical trials that have focused on leukaemia and sarcoma, which are predominantly p53 wild-type at diagnosis and are MDM2-amplified or have high expression of MDM2 [9]. Here, TP53 is linked to leukemia.