Prognostic significance of LINE-1 methylation level in esophageal squamous cell carcinoma.

Abstract

26 Background: Genome-wide DNA hypomethylation plays a role in genomic instability and carcinogenesis. DNA methylation in the long interspersed nucleotide element-1, L1 (LINE-1) repetitive element is a good indicator of global DNA methylation level. LINE-1 methylation is a useful marker for predicting cancer prognosis and monitoring efficacy of adjuvant therapy. Esophageal squamous cell carcinoma, the major histological type of esophageal cancer in East Asian countries, is one of the most aggressive malignant tumors. Nonetheless, prognostic significance of LINE-1 hypomethylaiton in esophageal cancer remains uncertain. Methods: Using 217 curatively resected esophageal squamous cell carcinomas, we quantified LINE-1 methylation using bisulfite-PCR-pyrosequencing assay. Cox proportional hazards model was used to calculate mortality hazard ratio (HR), adjusted for clinical, epidemiologic, and pathological variables. Results: Esophageal cancers showed significantly lower LINE-1 methylation level compared to matched normal esophageal mucosa (p<0.0001; N=50). Tumoral LINE-1 methylation ranged from 24.8 to 91.8 of 0-100 scale (N=217; mean 64.5; median 65.0; standard deviation 12.8). LINE-1 hypomethylation was significantly associated with disease-free survival [log-rank p=0.0008; univariate HR= 2.31, 95% confidence interval (CI) 1.38-3.84, p=0.0017; multivariate HR=1.81, 95% CI 1.06-3.05, p=0.031] and overall survival (log-rank p=0.0013; univariate HR=2.21, 95% CI 1.33-3.60, p=0.0026; multivariate HR=1.87, 95% CI 1.12-3.08, p=0.018]. Conclusions: LINE-1 hypomethylation in esophageal cancer is associated with shorter survival, suggesting its role as a prognostic biomarker. Given that epigenetic changes, including DNA methylation alterations, are reversible and can thus be targets for therapy or chemoprevention, our findings may have considerable clinical implications.