High EVI1 expression is associated with MLL rearrangements and predicts decreased survival in paediatric acute myeloid leukaemia: A report from the children's oncology group

Ectopic viral integration site-1 (EVI1) is highly expressed in certain cytogenetic subsets of adult acute myeloid leukaemia (AML), and has been associated with inferior survival. We sought to examine the clinical and biological associations of EVI1^high, defined as expression in excess of normal controls, in paediatric AML. EVI1 mRNA expression was measured via quantitative real-time polymerase chain reaction in diagnostic specimens obtained from 206 patients. Expression levels were correlated with clinical features and outcome. EVI1^high was present in 58/206 (28%) patients. MLL rearrangements occurred in 40% of EVI1^high patients as opposed to 12% of the EVI1^low/absent patients (P < 0·001). No abnormalities of 3q26 were found in EVI1^high patients by conventional cytogenetic analysis, nor were cryptic 3q26 abnormalities detected in a subset of patients screened by next-generation sequencing. French-American-British class M7 was enriched in the EVI1^high group, accounting for 24% of these patients. EVI1^high patients had significantly lower 5-year overall survival from study entry (51% vs. 68%, P = 0·015). However, in multivariate analysis including other established prognostic markers, EVI1 expression did not retain independent prognostic significance. EVI1 expression is currently being studied in a larger cohort of patients enrolled on subsequent Children's Oncology Group trials, to determine if EVI1^high has prognostic value in MLL-rearranged or intermediate-risk subsets.