TP53 and neuroblastoma: The PD profile was consistent with the PK profile, mechanism of action, and previous studies.11, 25, 27, 32 The analysis of PD biomarkers of response to RO6839921 alone showed changes in MIC‐1, p21, p53 and Ki67, consistent with our previous in vitro observations of idasanutlin mediated anti‐tumour activity.10 Our study is the only preclinical study of idasanutlin in neuroblastoma so far to include MIC‐1 as a PD biomarker, and demonstrated that in response to combination treatment MIC‐1 was the most responsive biomarker in the SHSY5Y‐Luc model and p21 in the NB1691‐Luc model.