MLL gene rearrangement, and not patient age, is the primary determinant of sensitivity to FLT3 inhibition in infant ALL. (A) MTT dose-response curves showing mean cytotoxic response to CEP-701 for infant and childhood ALL blasts, grouped by MLL gene status and age, normalized to untreated controls. Error bars represent standard error of the mean (SEM). (B) Dot plot of individual samples' MTT cytotoxic response at 50 nM CEP-701. Error bars show the group mean ± SEM. P values are from Student t test. Patient numbers (from Table 2) are noted next to each curve. H indicates Johns Hopkins patient; and J, St Jude patient.