NUP98-NSD1 Related Gene Expression Signature Is Strongly Associated with a Poor Prognosis in Pediatric Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a complex disease caused by mutations, epigenetic modifications, and deregulated expression of genes leading to increased proliferation and decreased differentiation of hematopoietic progenitor cells. Many important molecular markers have already been discovered in AML that have not only helped to better characterize patients, but also helped to improve risk stratification. However, in a subset of AML patients, no known prognosis-associated cytogenetic aberrations or mutations were detectable. In hematological malignancies, 11p15 translocations involving the nucleoporin 98-kDa (NUP98) protein gene are relatively rare, but more than 20 different chromosomal rearrangements have been identified. The cryptic t(5;11)(q35;p15.5), which is frequently accompanied by deletion of the long arm of chromosome 5, del(5q), creates a fusion gene between NUP98 and the nuclear receptor-binding SET-domain protein 1 (NSD1) gene. Recently, Hollink et al identified NUP98-NSD1 gene fusion by high-resolution genome-wide copy number analysis and reverse transcription (RT)-PCR in pediatric and adult AML patients, and reported that NUP98-NSD1 gene fusion was a predictor of poor prognosis. Thus, we explored the frequency, gene expression pattern, and clinical impact of NUP98-NSD1 in a large cohort of Japanese pediatric AML patients.

From January 2000 to December 2002, 318 patients were newly diagnosed with de novo AML. Of these, samples from 124 patients whose gene expression profiling data were available were analyzed, including 10 patients with FAB-M3 and 6 patients with Down syndrome (DS) who were treated on different treatment protocols. For the detection of NUP98-NSD1 gene fusion, direct sequencing was performed using an ABI PRISM 310 Genetic Analyzer (Applied Biosystems). Gene expression profiling data, which were performed before, were available for these 124 patients. Hierarchical clustering analysis was performed using Cluster and Tree View software.

NUP98-NSD1 fusion transcript was detected in 6 (4.8%) of 124 pediatric AML patients and a characteristic gene expression pattern related to these patients was also detected. Further hierarchical clustering analysis using the 87 probe sets which were differentially expressed in 6 NUP98-NSD1-positive patients did not detect a simple cluster of 6 NUP98-NSD1-positive patients but a relatively large cluster including 18 NUP98-NSD1-negative patients. When compared with 100 NUP98-NSD1 signature-negative patients, the 24 NUP98-NSD1 signature-positive patients frequently had normal karyotype (62.5%), and del(9q) (8.3%), but did not have any favorable chromosomal translocations such as t(8;21), inv(16) and t(15;17). The frequencies of M4 and M5 subtypes (14/24, P < 0.001) were also higher than those in NUP98-NSD1 signature-negative patients. In addition, they frequently had FLT3-ITD (12/24, P < 0.001), MLL-PTD (7/24, P = 0.124), NPM1 (3/24, P = 0.007) and WT1 (5/24, P = 0.037) mutations. In total, NUP98-NSD1 related gene expression signature (NUP98-NSD1 signature) represented 19% (24/124) of total patients and 58% (15/26) of cytogenetically normal patients in our cohort. Their 4-year overall survival (OS) and event-free survival (EFS) were poor when compared to 100 NUP98-NSD1 signature-negative patients (37.5% vs. 86.0% and 37.5% vs. 72.0%).

Our results indicated that Patients with NUP98-NSD1 related gene expression signature had extremely poor clinical outcome, irrespective of the presence of NUP98-NSD1 gene fusion. Most of the patients displaying the NUP98-NSD1 signature have been classified into an intermediate risk group, but their unfavorable outcome suggests that a high risk group is a more suitable stratification. These results suggest the presence of a new poor prognostic subgroup which revealed the value of the NUP98-NSD1 signature as prognostic markers in pediatric AML. Although further investigation is necessary, we believe that our work contributes to improve the risk stratification in pediatric AML.

No relevant conflicts of interest to declare.