Introduction and aim: Childhood cytogenetically normal acute myeloid leukemia (CN-AML) is a subgroup of pediatric AML lacking any known cytogenetic and abnormality. CN-AML accounts for 20% of pediatric AML and exhibits a very heterogeneous response to treatment and, consequently, variable outcome. With the aim of providing new insights into the molecular lesions of this subset of AML, we analyzed, through RNA-seq, 13 cases of pediatric CN-AML, corroborating our findings in an independent cohort of 152 AML patients enrolled in the AIEOP AML 2002/01 clinical trial.

Methods: Paired-end RNA-seq (75×2) was performed on PoliA(+) RNA extracted from blasts at diagnosis. ChimeraScan, deFuse and FusionMap algorithms were used for chimeric transcript detection.

Results: An alteration that was present in 2 out 13 cases was a chimeric transcript involving the genes nucleoporin 98kDa (NUP98) and PHD finger protein 23 (PHF23), resulting from a cryptic translocation t(11;17)(p15;p13). Both patients showed an in-frame fusion between exon 13 of NUP98 and exon 4 of PHF23 that was confirmed by RT-PCR analysis and Sanger sequencing. To date, the cryptic translocation t(11;17)(p15;p13) was never described before in pediatric AML and has been reported only once in an adult AML patient (Reader, et al. Leukemia 2007). In both our patients the same breakpoint in PHF23 gene at the beginning of exon 4 was present, which was different from that present in the adult patient.

To assess the incidence of NUP98-PHF23 fusion in pediatric CN-AML, then we studied by RT-PCR and Sanger sequencing a validation cohort of 152 CN-AML children negative for the most common recurrent cytogenetic and molecular lesions, i.e. those involving MLL, CBFB, NPM1 and FLT3. Overall, 2 out of the 152 CN-AML cases were found positive for NUP98-PHF23, demonstrating that this genomic aberrancy is not rare in pediatric CN-AML (tentative frequency 2.4%). Fluorescence in situ hybridization analysis confirmed the cryptic chromosomal translocation t(7;11)(p15;p13) leading to the fusion between NUP98 and PHF23 in all cases.

Conclusions: Lately, genome-wide approaches have been widely used to investigate the mutational landscape of CN-AML in adults. However, the genetic profile of childhood CN-AML still needs to be defined. Here, for the first time, we report the identification of a NUP98-PHF23 chimeric transcript in pediatric CN-AML. Together with recently published data demonstrating that NUP98-PHF23 promoted leukemogenesis and the observation that treatment with inhibitors of PHD-domain-mediated H3K4me3 binding, such as disulfiram (an FDA-approved drug), could selectively killed cells expressing NUP98-PHF23 (Gough, et al Cancer Discovery 2014), our findings enforce the role of epigenetic regulators in pediatric AML and suggest screening for this fusion gene at diagnosis in CN-AML pediatric patients.

Citation Format: Marco Togni, Riccardo Masetti, Martina Pigazzi, Annalisa Astolfi, Daniele Zama, Valentina Indio, Salvatore Serravalle, Elena Manara, Valeria Bisio, Sergio Rutella, Franca Fagioli, Giuseppe Basso, Andrea Pession, Franco Locatelli. NUP98-PHF23 is a novel fusion gene in pediatric cytogenetically normal acute myeloid leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-211. doi:10.1158/1538-7445.AM2015-LB-211