Abstract 2430: Neuroblastoma: Telomere elongation is responsible for aggressive behavior
Authors: Niloufar Javanmardi, Susanne Fransson, Rose-Marie Sjöberg, Anna Djos, Per Kogner, Tommy Martinsson
Journal: Cancer Research (2016)

Abstract Neuroblastoma (NB) is a highly malignant pediatric tumor of the sympathetic nervous system that commonly displays low overall mutation frequency. We searched for new structural rearrangements in a series of 275 NBs of all stages using high density SNP microarrays. Exome sequencing was also performed on 15 tumor/constitutional DNA pairs and 25 additional tumors, mainly high-risk NBs, using paired-end sequencing on Illumina instrument. Normalized coverage data were used to generate array comparative genomic hybridization (CGH)-like profiles. Structural rearrangements leading to gain of TERT gene were observed in 15 of 275 neuroblastomas as judged by SNP microarray. 12 out of these 15 tumors with TERT rearrangement belong to 11q-deleted subgroup of NB patients that marks tumors with a poor prognosis. These rearrangements occurred only in high-risk NBs in an almost mutually exclusive fashion with MYCN amplifications, which is a known genetic event in this tumor type. Furthermore, in the small series of NBs analyzed by exome sequencing, we detect extensive structural rearrangements of chromosome 2, 5 and 7 leading to amplification of MYCN, TERT and CDK6 respectively in one tumor. The exome sequencing approach detected at average 14 (range 2-77) somatic protein-changing alterations per tumor. Combining structural and mutational data from the exome sequencing show recurrent alterations in ATRX gene. In our NB cohort we see alterations of ATRX in four non MYCN-amplified tumors: two focal deletions, one nonsense mutation and one deleterious missense mutation. ATRX inactivation results in alternative lengthening of telomeres (ALT). This means that high-risk neuroblastomas cancer cells can preserve their telomeres by ALT or by activation of telomerase reverse transcriptase (encoded by TERT). Alterations in TERT and ATRX were mutually exclusive, which is in agreement with the independent activation by these genes of telomere lengthening. Moreover, three cases with chromothripsis of chromosome 5 with rearrangements affecting the TERT were identified through SNP microarrays. These results identify TERT as at least one of the target genes activated by chromothripsis of chromosome 5. This remodeling of the genomic context likely abrogates transcriptional silencing of TERT in high-risk neuroblastoma and places telomerase activation in the centre of transformation in a large fraction of these tumors. This study identifies recurrent TERT and ATRX rearrangements and telomere lengthening as an important mechanism characterizing high-risk tumors and it supports the pharmacological inhibition of these targets to improve the outcome for this patient group. Citation Format: Niloufar Javanmardi, Susanne Fransson, Rose-Marie Sjöberg, Anna Djos, Per Kogner, Tommy Martinsson. Neuroblastoma: Telomere elongation is responsible for aggressive behavior. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2430.