Abstract 5074: The impact of RHOA mutation related with invasion in diffuse-type gastric cancer
Authors: Eto Tsugio , Ishimoto Takatsugu , Izumi Daisuke , Tamaoki Yuka , Kuroda Daisuke , Arima Kota , kaida Takayoshi , Ohuchi Mayuko , Nakamura Kenichi , Tokunaga Ryuma , Shigaki Hironobu , Kurashige Junji , Iwatsuki Masaaki , Baba Yoshifumi , Sakamoto Yasuo , Yoshida Naoya , Baba Hideo 
Published: July 2016

Abstract
Background: Gastric cancer (GC) is one of the most general causes of cancer related death, especially in East Asia and is divided into intestinal type and diffuse type by Lauren classification. Five-year survival rate of diffuse-type gastric cancer (DGC) is poor compared with the Intestinal-type gastric cancer (IGC). To improve the prognosis of advanced GC patients, molecularly targeted drugs against gastric cancer have been developed including trastuzumab, a recombinant monoclonal antibody against HER2. But, HER2 gene amplification rate is about 10% in DGC, though 30% in IGC. DGC-specific molecular carcinogenic mechanisms have still remained unclear. Recently, some studies revealed RHOA mutations occur specifically in DGCs. They also demonstrated that proliferation and organoid formation are related with RHOA mutations in DGC. However, there is no report in terms of the functional difference among RHOA mutational hotspots in DGCs.
Aim: To investigate the functional difference among RHOA mutations and the impact on prognosis in DGCs.
Method: We prepared RHOA wild type vector and three RHOA mutation vectors (G17E, Y42C, and L57V). We introduced these RHOA vectors into DGC cell lines and examined invasion assay. In invasion assay of RHOA introduced DGC cell lines, we conducted experiments with or without TGFβ1 (RHOA activator).
Result: RHOA overexpression in DGC cells did not exhibit significant upregulation of invasiveness compared with empty vector introduced DGC cells. However, all RHOA mutation introduced DGC cells acquired more significant elevation of invasiveness as well as wild type after treatment with TGF-β1. (wild:p = 0.0001, G17E:p = 0.0001, Y42C:p = 0.0001, L57V: p&lt;0.0001). Among these RHOA mutations, G17E and Y42C RHOA mutation introduced DGC cells exhibited remarkable upregulation of invasiveness compared with wild type RHOA introduced DGCs (G17E:p&lt;0.0001 Y42C:p = 0.009).These results indicate particular RHOA mutations cause higher response to TGF-β1 compared with wild type.
Conclusion: We evaluated the functional difference among RHOA mutations in DGC. These results suggest particular RHOA mutation might have possibility to cause invasion in DGCs. A large cohort study across RHOA mutations in DGCs will be required to identify the clinical significance between hotspot RHOA mutations.
Citation Format: Tsugio Eto, Takatsugu Ishimoto, Daisuke Izumi, Yuka Tamaoki, Daisuke Kuroda, Kota Arima, Takayoshi kaida, Mayuko Ohuchi, Kenichi Nakamura, Ryuma Tokunaga, Hironobu Shigaki, Junji Kurashige, Masaaki Iwatsuki, Yoshifumi Baba, Yasuo Sakamoto, Naoya Yoshida, Hideo Baba. The impact of RHOA mutation related with invasion in diffuse-type gastric cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5074.