Abstract 4267: Integrated genomic analysis of hepatoblastoma identifies distinct molecular and prognostic subgroups

Hepatoblastoma (HB), the most common primary liver cancer in children, is a clinically heterogeneous embryonal malignancy. Previous studies of HB have revealed a paucity of genetic alterations in these tumors, other than mutations activating the WNT signaling pathway, and have not provided an adequate biological explanation for the diverse clinical outcomes of children with HB. To identify critical genes and pathways in the pathogenesis of HB and provide insight into the biologic basis and clinical heterogeneity of these tumors, we performed an integrated genomic analysis of a large cohort of clinically-annotated tumor-normal pairs utilizing whole exome sequencing (n = 35), mRNA and miRNA expression arrays (n = 51; n = 58), and high-resolution copy number arrays (n = 47). Somatic mutations/deletions of CTNNB1 or rare germline mutations of APC were identified in >90% of cases, confirming the central role of the WNT pathway in HB pathogenesis. The only other gene targeted by recurrent mutations in our cohort was the transcription factor NFE2L2 (NRF2), which was found to harbor hotspot mutations at a similar frequency (5-10%) to that reported for hepatocellular carcinoma. Expression profiling revealed near-universal WNT-pathway activation: 7 of the 20 most highly expressed genes in HB were WNT-pathway related genes, and the WNT-pathway marker DKK1 was expressed hundreds of standard deviations above its levels in normal liver. Unsupervised hierarchical clustering identified three distinct molecular HB clusters that were characterized by differential activation of hepatic progenitor cell and metabolic pathways. Analysis of the expression and/or inferred-activity of transcription factors and highly expressed genes identified prognostic biomarkers, including the significantly predictive regulons of NFE2L2, LIN28b, HNF1A, and NOTCH1. These were used to identify clinical groups that overlapped with HB expression clusters and were associated with patient survival. Tumors in the high-risk group were characterized by high NFE2L2, low NOTCH1 activity, and high LIN28b expression and activity (corresponding to low let-7b expression), as well as high expression of the onco-fetal proteins AFP and GPC3 and stem cell markers EPCAM, DLK1, and SALL4. In contrast, the low-risk group was characterized by high HNF1a and NOTCH1 activities and low LIN28 expression and activity. Rare chromosomal gains and losses were characteristic of the low risk group of tumors, while gains of 20q13 (SALL4) and 1q chromosomal regions were primarily found in the high and intermediate risk groups. Immunohistochemistry for LIN28b, NFE2L2, HNF1alpha, PTEN, and EPCAM is being performed on a validation set of tumors to assess their reliability to classify formalin-fixed tumor specimens. Prospective studies will test the prognostic utility of this method for children with HB. Citation Format: Dolores H. Lopez-Terrada, Pavel Sumazin, Yidong Chen, Lisa Trevino, Stephen Sarabia, Oliver Hampton, Kayuri Patel, Toni-Ann Mistretta, Barry Zorman, Sarah Comerford, David Wheeler, Murali Chintagumpala, Rebecka M. Meyers, Milton J. Finegold, Gail Tomlinson, Donald W. Parsons. Integrated genomic analysis of hepatoblastoma identifies distinct molecular and prognostic subgroups. [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 4267. doi:10.1158/1538-7445.AM2015-4267