Baseline MDM2 and day-5 plasma MIC-1 levels. (A) Baseline MDM2 levels were higher in patients with PV/ET compared with normal controls. The pretreatment MNC median MDM2 level was approximately fourfold higher in the PV/ET patients enrolled on the study compared with normal controls. (B) Plasma MIC-1 levels are increased on day 5 of idasanutlin therapy. p53 pathway activation is reflected by a 4.8-fold increase from baseline of MIC-1 protein levels by day 5 (P = .004).