Abstract 4264: Whole exome and targeted sequencing identified the MAPK and PI3K pathways as the main targets in intracranial and testicular germ cell tumors

Abstract

Abstract Intracranial germ cell tumors (iGCTs) are the second most common central nervous system tumors in patients under 14 in Japan. The majority of germinomas respond well to combined chemo- and radiotherapy, however non-germinoma germ cell tumors (NGGCTs) may show resistance to therapy and have a poor clinical outcome. Despite their clinical significance, the biology of iGCTs is mostly unknown. The aim of this study is to elucidate the molecular pathogenesis of iGCTs through a comprehensive genomic analysis. A total of 198 germ cell tumors (GCTs) including 133 iGCTs (69 pure germinomas, 56 NGGCTs and 8 metastatic tumors) as well as 65 testicular germ cell tumors (tGCTs) (39 seminomas and 26 non-seminoma GCTs) were collected from 13 centers participating in the Intracranial Germ Cell Tumor Consortium in Japan. Matched normal DNA was available for 70 iGCTs and 4 tGCTs. Somatic mutations in all coding exons were investigated by whole exome sequencing (WES) using SureSelectXT Human All Exon v4 and a GAIIx or HiSeq 2000 system in 41 tumors and the matched normal DNAs. Targeted sequencing with a set of custom made PCR primers was performed using either an IonTorrent PGM or Proton System. The results were integrated with the patients' clinical information that was available for 124 iGCT patients. Mutations in selected candidate genes were further evaluated in an independent tumor cohort using the IonTorrent PGM system. On average, 15.4 non-synonymous somatic mutations were observed in each tumor, ranging from 1 to 140 by WES in 41 iGCTs. Based on the WES data, 41 candidate genes were selected according to the frequency and/or significance of the mutations found. All coding exons of these 41 genes spanning over 160kb were PCR-amplified in a further 157 GCTs using the IonTorrent system. The combined WES and IonTorrent screenings showed that KIT was the most frequently mutated gene in both iGCTs (27%) and tGCTs (18%). MTOR was the second most frequently mutated also in both iGCTs (7%) and tGCTs (6%). RAS mutations (KRAS, HRAS, NRAS) were altogether found in 13% of iGCTs and 12% of tGCTs. These mutations were mutually exclusive to each other and also to KIT mutations. Collectively, the genes involved in the MAPK pathway (e.g., KIT, RAS, NF1) and the PI3K/MTOR pathway (e.g., MTOR, PTEN) were mutated in 44% and 13% of all GCTs. These alterations were significantly more common among pure germinomas than NGGCTs. The mutated MTOR protein was shown to have increased kinase activity, which was suppressed by a specific MTOR inhibitor. Our comprehensive mutational genomic analysis of GCTs revealed that alterations of the MAPK and/or PI3K/MTOR pathways play a critical role in the pathogenesis of both iGCTs and tGCTs, although the extent of their involvement depends on the histopathological subtypes. Our findings will hopefully lead to the development of a targeted therapy for treatment-resistant iGCTs. Citation Format: Koichi Ichimura, Shintaro Fukushima, Yasushi Totoki, Yuko Matsushita, Ayaka Otsuka, Arata Tomiyama, Tohru Niwa, Ryuichi Sakai, Toshikazu Ushijima, Taishi Nakamura, Tomonari Suzuki, Kouhei Fukuoka, Takaaki Yanagisawa, Kazuhiko Mishima, Yoichi Nakazato, Fumie Hosoda, Yoshitaka Narita, Soichiro Shibui, Akihiko Yoshida, Hirokazu Takami, Akitake Mukasa, Koki Aihara, Nobuhito Saito, Toshihiro Kumabe, Masayuki Kanamori, Teiji Tominaga, Keiichi Kobayashi, Saki Shimizu, Motoo Nagane, Toshihiko Iuchi, Masahiro Mizoguchi, Koji Yoshimoto, Kaoru Tamura, Taketoshi Maehara, Kazuhiko Sugiyama, Mitsutoshi Nakada, Keiichi Sakai, Yonehiro Kanemura, Masahiro Nonaka, Kiyotaka Yokogami, Hideo Takeshima, Nobutaka Kawahara, Tatsuya Takayama, Masahiro Yao, Hiromi Nakamura, Natsuko Hama, Masao Matsutani, Tatsuhiro Shibata, Ryo Nishikawa. Whole exome and targeted sequencing identified the MAPK and PI3K pathways as the main targets in intracranial and testicular germ cell tumors. [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 4264. doi:10.1158/1538-7445.AM2014-4264