High Expression of Neutrophil Elastase Predicts Improved Survival In Pediatric Acute Myeloid Leukemia: A Report From the Children's Oncology Group

Recent studies indicated that high expression of neutrophil elastase, a primary granule serine protease encoded by ELANE (ELA2), predicts longer survival of patients with chronic-phase chronic myeloid leukemia (CML) and improved outcome following allogeneic hematopoietic stem cell transplantation for advanced-phase CML. In contrast, the prognostic role of neutrophil elastase in acute myeloid leukemia (AML) is unknown. Therefore, we evaluated its expression in participants in a recent Children's Oncology Group (COG) AML pilot protocol.

COG-AAML03P1 enrolled 340 newly diagnosed children (aged 1 month to 21 years) with de novo AML, excluding those with acute promyelocytic leukemia and Down syndrome, and tested the feasibility of combining gemtuzumab ozogamicin (GO) with intensive induction chemotherapy followed by GO-containing intensification therapy or matched related donor stem cell transplantation. Diagnostic marrow specimens from 113 randomly selected patients were used for ELANE mRNA quantification using a sandwich nucleic acid hybridization method employing branched DNA molecules to amplify the signal from captured target RNA. Expression levels were normalized using beta glucuronidase (GUSB) and then correlated with patient demographics, laboratory characteristics, and clinical outcome. Cytogenetics and molecular prognostic markers were used for risk classification as follows: low risk (mutation in core-binding factor, NPM1, or CEBPa; n=43), high risk (−5/5q−, monosomy 7, or FLT3-ITD with high allelic ratio; n=16), or standard risk (all other patients with cytogenetic/molecular data; n=54).

Among the 113 diagnostic specimens, ELANE mRNA expression levels were undetectable in 3 samples and varied more than 70,000-fold relative to GUSB in the rest, from 0.0005 to 36.32 (median, 0.89). Patients with high ELANE expression (>median expression) were more likely to have myelomonocytic cell characteristics (FAB M4, p<0.001) and more likely to have core-binding factor translocations, t(8;21) (p=0.05) or inv(16) (p<0.003). They had a lower prevalence of megakaryocytic leukemia (p<0.02). There was no difference in the prevalence of FLT3-ITD or NPM1 mutations. As a result of these characteristics, patients with high ELANE expression were more likely to have low-risk disease (p<0.001) at the expense of standard-risk disease, while the prevalence of high-risk disease was similar. We subsequently determined the clinical outcome per median ELANE expression for the entire cohort as well as the specific risk groups. In the entire cohort, patients with high ELANE expression had a significantly superior 3-year overall survival (OS; 80±11% vs 61±13%, p=0.045) and tended to have better disease-free survival (66±14% vs 51±16%, p=0.118). Subgroup analyses were limited by the small sample size. Nevertheless, in both high- and low-risk disease, patients with high ELANE expression tended to have a better 3-year OS than patients with low ELANE expression (67±38% vs 30±29%, p=0.308 for high risk; 90±11% vs 75±25%, p=0.361 for low risk). By comparison, OS in standard-risk patients appeared similar for patients with high and low ELANE expression (70±21% vs 66±17%, p=0.849). In multivariate Cox regression analyses that included age, cytogenetics, and molecular prognostic factors, high ELANE expression was associated with reduced overall mortality (hazard ratio: 0.66); however, this result did not reach statistical significance (95% confidence interval: 0.33–1.35, p=0.260), possibly because of the small sample size.

This study revealed significant heterogeneity of ELANE expression in pediatric AML and its association with improved OS. This association is at least partly due to the high proportion of AMLs with core-binding factor aberrations in patients with high ELANE expression. Nevertheless, high ELANE expression may predict improved OS even within specific risk groups, in particular high-risk disease, although further studies with a larger patient cohort will be necessary to confirm this finding.

No relevant conflicts of interest to declare.