Abstract 893: Diffuse gastric adenocarcinoma often harbors KMT2C mutations resulting in malignant phenotypes and worse overall survival

Abstract

Abstract Purpose: The Lauren diffuse type of gastric adenocarcinoma (DGA) is genomically stable compared to the intestinal type, but the primary driver mutations in DGA are still being defined. Lysine (K) -specific methyltransferase 2C (KMT2C), also known as mixed lineage leukemia 3 (MLL3), is a histone methyltransferase involved in transcriptional coactivation and can be mutated in gastric cancer. The purpose of this study was to determine the frequency of KMT2C mutation in DGA and to elucidate the role of KMT2C in DGA tumorigenesis and progression. Methods: Whole exome sequencing was performed on matched tumor samples of 27 patients with DGA who underwent potentially curative surgical resection. Immunohistochemistry (IHC) was performed for KMT2C protein expression on these same tumors and on an additional 289 tumors from a separate cohort of patients with DGA. KMT2C overexpression in DGA cell lines (MKN-45 and SNU-668) using lentiviral transduction and KMT2C shRNA knockdown in normal gastric epithelial cells were examined in several in vitro assays. Results: Thirty-eight percent of the 27 sequenced DGA specimens harbored somatic mutations in KMT2C. The next most frequent mutation, CDH1, which encodes E-cadherin, was found in 28% of specimens. Patients with KMT2C mutation tended to have worse overall survival (OS) compared to patients without the mutation (p = 0.194). Additional tumor tissue for IHC analysis was only available from 11 of 27 patients. Among this group, patients with tumors expressing KMT2C protein had better OS compared to patients whose tumors did not express KMT2C (p = 0.034). In an external validation set of 289 DGA samples, KMT2C expression again correlated with better OS (p = 0.009). In the DGA cell lines, KMT2C overexpression reduced proliferation by 32-39%, soft agar colony formation by 75-77%, spheroid cell formation by 77-78%, cell migration by 52-60%, and cell invasion by 50-74%. KMT2C overexpression also increased resistance to 5-FU and cisplatin chemotherapy. KMT2C shRNA knockdown in gastric epithelial cells increased proliferation, soft agar colony formation, migration, and invasion by 1.7- to 25-fold. Conclusions: KMT2C is frequently mutated in DGA, and loss of KMT2C protein expression correlates with worse OS. Restoration of KMT2C expression in DGA cell lines reduces cancer stem-like cell and malignant phenotypes. Thus, KMT2C may be a novel therapeutic target for patients with DGA. Citation Format: Soo-Jeong Cho, Changhwan Yoon, Jun Ho Lee, Kevin K. Chang, Bulent A. Aksoy, Do Joong Park, Sam S. Yoon. Diffuse gastric adenocarcinoma often harbors KMT2C mutations resulting in malignant phenotypes and worse overall survival. [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 893.