Baseline tumour MDM2 expression may be important as clinical response to idasanutlin in AML patients has been associated with baseline MDM2 expression in leukaemic blasts.48 In conclusion, our study provides valuable PK, PD and efficacy data of IV RO6839921 as well as potential mechanisms of synergy to support the paediatric assessment of IV or oral idasanutlin, alone and in combination with a temozolomide backbone to provide a novel therapeutic strategy for patients with relapsed/refractory high‐risk neuroblastoma. Here, MDM2 is linked to neuroblastoma.