Abstract 3429: Genetic analysis of pancreatic neuroendocrine neoplasms grade 3
Authors: Kakiuchi Nobuyuki , Yoshida Kenichi , Shiozawa Yusuke , Yokoyama Akira , Kataoka Keisuke , Inoue Yoshikage , Takeuchi Yasuhide , Hirano Tomonori , Fujii Yoichi , Ueno Hiroo , Hijioka Susumu , Mizuno Nobumasa , Hosoda Waki , Yatabe Yasushi , Chiba Kenichi , Tanaka Hiroko , Shiraishi Yuichi , Miyano Satoru , Masui Toshihiko , Uemoto Shinji , Yoshizawa Akihiko , Haga Hironori , Uza Norimitsu , Seno Hiroshi , Kodama Yuzo , Ogawa Seishi 
Published: August 2019

Pancreatic neuroendocrine neoplasms (PanNENs) are pancreatic tumors with neuroendocrine differentiation. PanNENs are classified into three grades according to the proliferating cell fraction as measured by Ki-67 or mitotic index. Among them, PanNEN grade 3 (PanNEN G3) shows the highest Ki-67 index &gt; 20%, which is morphologically divided into two categories, well-differentiated (PanNET G3) and poorly differentiated (PanNEC) tumors. Although sharing some overlapping histological features, both tumors also differ from each other with respect of clinical characteristics. To date, the molecular basis of these difference and similarity are poorly understood. To understand their molecular pathogenesis, we performed comprehensive genetic analysis on PanNEN G3.

In total, we enrolled 25 PanNEN G3 cases, including 13 PanNET G3, 10 PanNEC, and 2 PanNEN G3 NOS, which were analyzed for somatic mutations. All tumors showed neuroendocrine markers such as synaptophysin or chromogranin A. The median Ki67 index of PanNET G3 was 30.5% (15-78%), which was lower than that of PanNEC (median 70.9%, range 44-100 %). Genomic DNA was extracted from microdissected tumors and paired normal tissues from formalin-fixed paraffin-embedded PanNEN G3 specimens guided by H&E stained sections and subjected to whole-exome sequencing (WES). Copy number alterations were also analyzed on the basis of sequencing data. All tumor specimens were centrally reviewed by the two expert pathologists and assigned to PanNET G3, PanNEC, or PanNEN G3 not otherwise specified (PanNEN G3 NOS).

WES analysis detected a total of 1,688 somatic mutations with a median of 45 (range 21-450)/sample. There was no clear difference in mutational burden between PanNET G3 and PanNEC. Combined with copy number alterations, mutations most frequently affected TP53 (40%), followed by MEN1(28%), SMAD4 (28%), KRAS(24%), and CDKN2A (20%). Frequently mutated in PanNET G1/2, MEN1, DAXX, and ATRX mutations were associated with well-differentiated morphology (n=7/7), while tumors with KRAS or RB1 mutations exhibited poorly differentiated histology (n=5/5). MEN1, DAXX, and ATRX mutations frequently co-occurred with mutations in mTOR pathway genes, such as NF1, TSC2, or DEPDC5 (q&lt;0.001), suggesting that some PanNET G3 might evolve from PanNET G1/2 by acquiring mutations that activate the mTOR pathway. Whereas, in PanNEC, MEN1, DAXX, and ATRX had never been mutated and KRAS and RB1 are recurrently mutated. Therefore, PanNEC does not derive from PanNET and it occurs independently. In survival analysis of PanNEN G3, SMAD4 mutation as well as high grade pathology was significantly contributed to shorter overall survival.

Our results help understand a molecular basis of PanNEN G3, contributing to a better understanding and classification of PanNET G3 and PanNEC.

Citation Format: Nobuyuki Kakiuchi, Kenichi Yoshida, Yusuke Shiozawa, Akira Yokoyama, Keisuke Kataoka, Yoshikage Inoue, Yasuhide Takeuchi, Tomonori Hirano, Yoichi Fujii, Hiroo Ueno, Susumu Hijioka, Nobumasa Mizuno, Waki Hosoda, Yasushi Yatabe, Kenichi Chiba, Hiroko Tanaka, Yuichi Shiraishi, Satoru Miyano, Toshihiko Masui, Shinji Uemoto, Akihiko Yoshizawa, Hironori Haga, Norimitsu Uza, Hiroshi Seno, Yuzo Kodama, Seishi Ogawa. Genetic analysis of pancreatic neuroendocrine neoplasms grade 3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3429.