Abstract 1370: Epigenetic clustering of gastric carcinoma based on DNA methylation profiles at the precancerous stage: its correlation with tumor aggressiveness and patient outcome
Authors: Yamanoi Kazuhiro , Arai Eri , Takahashi Yoriko , Miyata Sayaka , Kushima Ryoji , Katai Hitoshi , Sakamoto Michiie , Kanai Yae 
Published: May 2015

Abstract
Aim: The aim of this study was to clarify the significance of DNA methylation alterations during gastric carcinogenesis.
Background: DNA methylation alterations are induced by carcinogenetic factors at the precancerous stage in various organs. As for gastric mucosae, aberrant DNA methylation is considered to be induced by Helicobacter pylori, Epstein-Barr virus and other carcinogenetic factors. Since field cancerization concept has become evident in the stomach, non-cancerous gastric mucosae obtained from patients with gastric carcinomas (GCs) can be at the precancerous stage. However, correlations between DNA methylation profiles in such non-cancerous gastric mucosae at the precancerous stage and clinicopathological aggressiveness of GCs developing in the individual same patients and patient outcome have not been clarified.
Methods: Single-CpG resolution genome-wide DNA methylation analysis using the Infinium HumanMethylation27 Bead Array (Illumina) was performed in 110 paired samples of non-cancerous gastric mucosa (N) and tumorous tissue (T) from patients with GCs.
Results: DNA methylation alterations on 3,877 probes occurred in T samples relative to N samples. Since Ns can be at the precancerous stage according to field cancerization concept, we first focused on DNA methylation levels in N samples (βN) and performed unsupervised hierarchical clustering using βN on the 3,877 probes. 110 patients with GCs were subclustered into Cluster A (n=20), Cluster B1 (n=20) and Cluster B2 (n=70). GCs belonging to Cluster B1 more frequently showed undifferentiated histology and higher pT stage and pathological TNM stage when compared to those in Clusters A and B2. Recurrence-free and overall survival rates of patients in Cluster B1 were lower than those of patients in Clusters A and B2. Sixty hallmark genes of which βN characterized the epigenetic clustering were identified. To examine whether DNA methylation profiles in N samples were inherited by GCs themselves, we next focused on DNA methylation levels of the 60 hallmark genes in T samples (βT). In 43 out of the 60 hallmark genes, βT was again significantly correlated with undifferentiated histology or higher pT stage and pathological TNM stage. In 25 and 26 out of the 60 hallmark genes, βT was significantly correlated with recurrence-free and overall survival rates of the 110 patients, respectively. Multivariate analyses using Cox proportional hazards regression model revealed that βT in 10 out of the 60 hallmark genes were a significant prognostic factor which was independent from histological differentiation, pT stage and pathological TNM stage.
Conclusion: These data indicated that DNA methylation profiles at the precancerous stage may be inherited by GCs themselves and may determine tumor aggressiveness and patient outcome.
Citation Format: Kazuhiro Yamanoi, Eri Arai, Yoriko Takahashi, Sayaka Miyata, Ryoji Kushima, Hitoshi Katai, Michiie Sakamoto, Yae Kanai. Epigenetic clustering of gastric carcinoma based on DNA methylation profiles at the precancerous stage: its correlation with tumor aggressiveness and patient outcome. [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 1370. doi:10.1158/1538-7445.AM2014-1370