PS02.176: LINE-1 METHYLATION LEVEL AND LOCAL IMMUNE RESPONSE IN ESOPHAGEAL CANCER

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Abstract Background In cancer cells, DNA methylation may be altered in two principle ways; global DNA hypomethylation and site-specific CpG island promoter hypermethylation. Since Long interspersed element-1 (LINE-1 or L1; a repetitive DNA retrotransposon) constitutes a substantial portion (approximately 17%) of the human genome, the extent of LINE-1 methylation is regarded as a surrogate marker of global DNA methylation. In previous studies, we demonstrated that LINE-1 hypomethylation was strongly associated with a poor prognosis in esophageal cancer, supporting its potential role as a prognostic marker (Ann Surg 2012). We also found that LINE-1-hypomethylated tumors showed highly frequent genomic gains at various loci containing candidate oncogenes such as CDK6 (Clin Cancer Res 2014). Given that immunotherapy, as represented by PD-1/PD-L1-targeting antibodies, has increasingly gained attention as a novel treatment strategy for esophageal cancer, better understanding of local immune response status in esophageal cancer is important. The aim of this study is to evaluate the relationship between LINE-1 methylation level and local immune response in esophageal cancer. Methods Using a non-biased database of 305 curatively resected esophageal cancers, we evaluated PD-L1 expression and TIL status (CD8 expression) by immunohistochemical analysis (Ann Surg 2017). Results TIL positivity was significantly correlated with longer overall survival (log-rank P < 0.0001). TIL-negative cases demonstrated significantly lower LINE-1 methylation level compared with TIL-positive cases (P = 0.012). This finding certainly supports that LINE-1 methylation level may influence the local immune response status. Conclusion PD-L1 expression was not related with LINE-1 methylation level. Further investigations in this field would provide deeper insights into esophageal tumor immunology and assist the development of new therapeutic strategies against esophageal cancer. Disclosure All authors have declared no conflicts of interest.