Whole-transcriptome analysis in acute lymphoblastic leukemia: a report from the DFCI ALL Consortium Protocol 16-001

Abstract

The molecular hallmark of childhood ALL is characterized by recurrent, prognostic genetic alterations, many of which are cryptic by conventional cytogenetics. RNA-seq is a powerful next-generation sequencing technology with the ability to simultaneously identify cryptic gene rearrangements, sequence mutations and gene expression profiles in a single assay. We examined the feasibility and utility of incorporating RNA-seq into a prospective multi-center phase 3 clinical trial for children with newly-diagnosed ALL. Patients enrolled on the DFCI ALL Consortium Protocol 16-001 who consented to optional studies and had available material underwent RNA-seq. RNA-seq was performed in 173 ALL patients. RNA-seq identified at least one alteration in 157 (91%) patients. Fusion detection was 100% concordant with results obtained from conventional cytogenetic analyses. An additional 56 gene fusions were identified by RNA-seq, many of which confer prognostic or therapeutic significance. Gene expression profiling enabled further molecular classification into the following B-ALL subgroups: High hyperdiploid (n=36), ETV6-RUNX1/-like (n=31), TCF3-PBX1 (n=7), KMT2A-rearranged (n=5), iAMP21 (n=1), hypodiploid (n=1), BCR-ABL1/-like (n=16), DUX4-rearranged (n=11), PAX5 alterations (n=11), PAX5 P80R (n=1), ZNF384-rearranged (n=4), NUTM1-rearranged (n=1), MEF2D-rearranged (n=1) and Others (n=10). RNA-seq identified 141 nonsynonymous mutations in 93 (54%) patients; the most frequent were RAS-MAPK pathway mutations. Among 79 patients with both low-density array and RNA-seq data for the Ph-like gene signature prediction, results were concordant in 74 (94%) patients. In conclusion, RNA-seq identified several clinically-relevant genetic alterations not detected by conventional methods, supporting the integration of this technology in frontline pediatric ALL trials.