FLT3 and acute lymphoblastic leukemia: Consistent with the TARGET-ALL Phase2 cohort, transcriptional profiling of patient-derived xenografts (PDX) obtained from the Pediatric Preclinical Testing Consortium (PPTC) [45–47] showed that ETP-ALL displayed the highest FLT3 expression with elevated mRNA levels in 5 out of 6 ETP but only 1 out of 19 other more mature T-ALL samples (Fig. 3B).