Abstract 5167: Identification of inactivating mutations in stepwise hepatocarcinogenesis using next generation sequencer
Authors: Midorikawa Yutaka , Yamamoto Shogo , Ueda Hiroo , Sonoda Kotaro , Tsuji Shingo , Tatsuno Kenji , Shibata Tatsuhiro , Covington Kyle , Wheeler David , Takayama Tadatoshi , Aburatani Hiroyuki 
Published: May 2015

Abstract
Early hepatocellular carcinoma (HCC) is histologically diagnosed as the existence of intratumoral portal tracts with stromal invasion. It consists of small hepatocytes with little cellular atypia but with structural atypia. This type of very well-differentiated cancerous tissue is usually characterized by indistinct margins and many portal tracts within the tumor, and develops into classical HCC. To identify sequential genomic changes in stepwise hepatocarcinogenesis, we analyzed fusion genes and mutations using next generation sequencer about 43 early and 105 advanced HCCs. First, exome sequence showed that base sequence aberrations (non-silent) were more frequent in advanced HCC than early HCC (70.9 ± 29.0 vs 53.7 ± 23.8 genes per tumor, P = 0.0002). Mutations in p53/RB pathway including TP53, ATM, RB1, CDKN2A, and CDKN1A were observed in 27.9% and 38.1% in early and advanced HCCs, respectively (P = 0.161) and those of WNT/b-catenin pathways consisting of CTNNB1, AXIN1, and APC were recurrently observed in both early and advanced HCCs (27.9% vs 41.0%, P = 0.095). On the other hand, mutations in SWI/SNF complex genes were more frequently observed in advanced HCC (35.2%) than early HCC (16.3%, P = 0.016). Especially, inactivating mutation of ARID was found in 16 advanced HCCs (15.2%) while only 1 case in early HCC (2.3%, P = 0.018). Consistent with our previous report homozygous deletions near CSMD1 and CDKN2A were also found in 8 and 5 cases, respectively, only in advanced HCC. Next, we detected 4 types of fusion gene, including interchromosomal (translocation), intrachromosomal (deletion), intrachromosomal (translocation), and inversion by RNA sequencing. We also found that every HCC harbored 2 to 5 fusion genes, which were more frequent in advanced than early
HCC, although there were no recurrent rearrangements in neither advanced nor early HCCs. Especially chromathripsis, in which 10 to 100 rearrangements were localized in the specific genomic regions and genomic features imply chromosome breaks occur in one-off crisis, was the event observed only in advanced HCC. Taken together, genomic changes were more frequent in advanced HCC, and inactivating mutations of p53/RB and WNT/b-catenin signaling pathways are the driver mutation in the initiation of hepatocarcinogenesis and that of ARID2 may play pivotal roles in the progression from early to advanced HCC.
Citation Format: Yutaka Midorikawa, Shogo Yamamoto, Hiroo Ueda, Kotaro Sonoda, Shingo Tsuji, Kenji Tatsuno, Tatsuhiro Shibata, Kyle Covington, David Wheeler, Tadatoshi Takayama, Hiroyuki Aburatani. Identification of inactivating mutations in stepwise hepatocarcinogenesis using next generation sequencer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5167. doi:10.1158/1538-7445.AM2014-5167