Abstract B56: Genomic background of neuroblastomas with intratumor heterogeneity of MYCN amplification

Abstract

Abstract Background: MYCN amplification (MNA) is the most powerful therapy-stratifying marker in neuroblastoma (NB). With recent technological advances and the analysis of different pieces of individual tumors it became evident that approximately 20% of MYCN amplified NBs carry the amplification in only a fraction of tumor cells ranging from a few amplified cells to up to the majority (∼70%) of all tumor cells. Although the existence of intratumor heterogeneity of MNA (hetMNA) is well known today, its clinical meaning is still unclear, compromising the patients' assignment to specific treatment strategies. To learn whether the genomic background of hetMNA tumors differs to the genomic background of homogenously MNA (homMNA) tumors and non-amplified NBs, we looked for common segmental and numerical chromosome aberrations, allelic imbalances and the expression of the favorable NB marker (CD44). Material and methods: Ultra-high resolution SNParray analyses (2.6 million copy number markers) and interphase FISH on various tumor and bone marrow samples (BM) obtained from 20 hetMNA, 22 homMNA and 110 nonMNA NB patients were performed. Median patient age of the hetMNA patients group was 13.5 months (range 6-168), 13 patients were below and 7 above 18 months of age. CD44 staining was done by fluorescence labeled antibodies on cryo-sections. Results: Besides hetMNA, seven tumors showed no segmental chromosomal aberrations (noSCA), another four were heterogeneous concerning both, MNA and SCA (hetSCA), one with two SCAs and eight exhibited a high number (>7) of SCAs (highSCA) from these eight one with chromothripsis and two with deletions within the ATRX1 gene. Acquired whole chromosome uniparental disomy (wcUPD) occurred in 15/20 (75%) of hetMNA tumors, in 4/22 (18.2%) homMNA tumors and in 38/110 (34.5%) of the nonMNA NBs. wcUPD of chromosome 11 was predominately found in the hetMNA group (10/15), three out of four in the homMNA group and 7/38 in the nonMNA group also showed wcUPD11. The increase of SCAs correlated with age (no/hetSCA: 11/13 infants and highSCA: 7/7 patients >18m). By contrast, UPD11 decreased with age (UPD11: 9/13 infants and 1/7 patients >18m). Furthermore, hetMNA tumors were frequently CD44+, which is not the case in homMNA tumors. Conclusions: The high frequency of wcUPDs, especially UPD11, in hetMNA tumors has not been described so far and could represent a hallmark of hetMNA NBs. Moreover, it was unexpected that hetMNA tumors in contrast to homMNA tumors can either totally lack SCAs or also bear a multitude of them. This data provide a more complete picture of the tumor genomics landscape portrayed from single tumor-biopsy. Citation Format: Inge M. Ambros, Clemens Brunner, Dominik Bogen, Gabriele Amann, Reza Abbasi, Barbara Gürtl-Lackner, Michael D. Hogarty, Tommy Martinsson, Martin Bilban, Ruth Ladenstein, Peter F. Ambros. Genomic background of neuroblastomas with intratumor heterogeneity of MYCN amplification. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B56.