FL levels and in vivo FLT3 inhibition. (A) Plasma FL levels determined by enzyme-linked immunosorbent assay using samples collected from the current trial of 5-azacitidine/sorafenib (solid columns). For comparison (hatched columns) is shown FL levels from plasma samples collected from relapsed/refractory FLT3-ITD AML patients on the Cephalon 204 trial²⁴  2 or 4 weeks after starting salvage chemotherapy (mitoxantrone/etoposide/cytarabine). (B) FLT3 inhibition grouped according to treatment time point. PIA assays (see Materials and methods) were performed on individual plasma samples collected during therapy. Densitometry measurements from individual FLT3 PIA assays are plotted against time point. The solid lines indicate the mean level of P-FLT3 for the patient group at each time point. C, cycle; D, day.