Variation in FLT3 PIA over time. FLT3 PIA assay was performed as described in “Patients, materials, and methods.” For each patient the 4 histogram columns show the FLT3 PIA, which was measured prior to commencement of lestaurtinib treatment and predosing on trial days 14, 28, and 56. *Clinically responsive patients (hematologic response or greater). No clinical responses were seen in patients who failed to demonstrate more than 85% sustained FLT3 PIA.