Retrospective Evaluation of Correlations Between Genetic Backgrounds and Stem Cell Transplantation for De Novo Pediatric Acute Myeloid Leukemia: A Study from the Japan Pediatric Leukemia/Lymphoma Study Group (JPLSG) AML-05 Clinical Trial

Introduction

Pediatric acute myeloid leukemia (AML) comprises less than 20% of pediatric leukemia, representing one of the major therapeutic challenges in pediatric oncology. Approximately 40% of patients still have a relapse after first-line therapies, and the expected long-term survival rate decreases following relapse. Stem cell transplantation (SCT) was a conclusive strategy for de novo AML patients with a high risk and relapsed or refractory patients with standard and intermediate risk in a recent clinical trial. AML is a molecularly and clinically heterogeneous disease caused by various genetic alterations. Thus, it is difficult to accurately evaluate risk stratification even if known representative molecular markers, including KIT, FLT3-ITD, t(8;21)/RUNX1-RUNX1T1, and KMT2A (also known as MLL)-rearrangements, are used.

Methods

We investigated differences in the genetic background between SCT and non-SCT groups in participants of the Japan Pediatric Leukemia/Lymphoma Study Group (JPLSG) AML-05 trial. Among 369 patients with de novo AML, 175 patients received SCT. A standardized form was used to record clinical variables, including patient demographic information. The clinical data of patients in each risk group were followed for 3 years after the date of final registration. JPLSG performed a central review of morphologic classification and karyotyping based on the World Health Organization Classification, French-American-British classification, and cytogenetic analysis using conventional G-banding. Molecular characterization included mutational analyses of KIT (exons 8 and 17), N- and K-RAS (exons 1 and 2), NPM1 (exon 12), CEBPA (exon 12), FLT3-ITD, NUP98-NSD1,and CBFA2T3-GLIS2 gene rearrangement, as well as KMT2A- partial tandem duplication (MLPA methods). We also evaluated the gene expression of MECOM (also known as EVI1) and PRDM16 (also known as MEL1) because their high expressions are known poor prognostic markers. Overall survival (OS) was defined as the time from AML diagnosis to death or censorship at the last follow-up. Event-free survival (EFS) was defined as the time from AML diagnosis to treatment failure, relapse, death, or last follow-up.

Results

The 3-year OS among SCT patients (n = 175) was approximately 50%. It was significantly worse than that of non-SCT patients (n = 194, 90%; P < 0.001). Among 137 CBF-AML patients, 44 patients (32%) received SCT and their 3-year OS was 80%. On the other hand, among 232 non-CBF-AML patients, 131 patients (57%) received SCT, and their 3-year OS was only 35%. This result indicated that SCT is beneficial for relapsed CBF-AML, whereas most non-CBF patients who received SCT did not obtain the clinical benefit. In terms of the molecular characteristics, among 58 patients with high EVI1 expression, 39 patients (67%) received SCT, and their 3-year OS was approximately 35%. EVI1 expression was especially useful when using with MLL rearrangement because prognosis of patients with both MLL rearrangement andhigh EVI1 expression were extremely poor. On the other hand, among 84 patients with high PRDM16 expression, 63 patients (75%) received SCT, and their 3-year OS was approximately 20%. Although all AML patients with FLT3-ITD were assigned to receive SCT in the AML-05 trial, FLT3-ITD(+) patients withlow PRDM16 expression had a better outcome than FLT3-ITD(+) patients with high PRDM16 expression (3-year OS: 70% vs. 21%; P < 0.001). This result indicated that FLT3-ITD itself might not necessarily be associated with poor prognosis. PRDM16 gene expression is a useful marker to select patients needing SCT, particularly for patients with FLT3-ITD.

Conclusion

SCT was beneficial for patients with CBF-AML, whereas SCT was insufficient to rescue patients with non-CBF AML who relapsed, particularly patients with both FLT3-ITD(+) and high PRDM16 expression. New strategies, such as gemtuzumab ozogamicin or haploidentical SCT, are urged to rescue high risk/refractory patients.