Abstract 1357: Clinical, pathological and prognostic value of LINE-1 methylation in hepatocellular carcinoma
Authors: harada kazuto , Baba Yoshirumi , Chikamoto Akira , Ishimoto Takatsugu , Kosumi Keisuke , Murata Asuka , Yoshida Naoya , Beppu Toru , Baba Hideo 
Published: May 2015

Objectives:Cancer cells exhibit 2 types of deoxyribonucleic acid (DNA) methylation alterations: genome-wide DNA hypomethylation and site-specific CpG island promoter hypermethylation. Genome-wide DNA hypomethylation plays a role in genomic instability and carcinogenesis. As long interspersed nucleotide element-1 (LINE-1) retrotransposon constitutes a substantial portion (approximately 17%) of the humangenome, the level of LINE-1 methylation is regarded to be a surrogate marker of genome-wide DNA methylation. Importantly, LINE-1 hypomethylation is associated with poor prognosis in several type of cancers, suggesting the potencial role of the LINE-1 methylation level as a useful marker for predicting cancer prognosis. However, clinical, pathological and prognostic significance of LINE-1 hypomethylaiton in hepatocellular carcinoma (HCC) remains unclear.

Methods: Using 160 HCC resected specimens, we quantified the LINE-1 methylation by utilizing the bisulfite pyrosequencing technology. This assay amplifies a region of LINE-1 element (position 305-331 in accession no. X58075), which includes 4 CpG cites. The average of the relative amounts of C in the 4 CpG sites was used as the overall LINE-1 methylation level.Results: We first examined the LINE-1 methylation level in 85 HCC tissues and matched normal hepatic parenchyma samples. The cancer tissues exhibited significantly lower levels of LINE-1 methylation (median, 64.5 ; range, 99.1-21.5) than the matched normal hepatic parenchyma (median, 81.0 ; range, 97.2-35.8) (P &lt; 0.0001 by the paired t test). The LINE-1 methylation level of HCC was not associated with any of theclinical, epidemiological, or pathological characteristics, including sex, age, AFP, PIVKA-II, infection of hepatitis B virus and hepatitis C virus, ICG-R15, stage of fibrosis, differentiation, tumor size, tumor type, vascular invasion and stage (all P &gt; 0.09). In the Kaplan-Meier analysis, LINE-1 hypomethylators (methylation level &lt; 74.4) experienced significantly shorter disease-free survival than those with hypermethylators (log-rank P=0.029). Over-all survival is not associated with LINE-1 methylation ( log-rank P=0.16).

Conclusions: Genome-wide DNA hypomethylation, as measured in LINE-1, is associated with disease-free survival among patients with HCC, suggesting that LINE-1 hypomethylation may be a biomarker that can be used to identify patients who will experience an inferior outcome.

Citation Format: kazuto harada, Yoshirumi Baba, Akira Chikamoto, Takatsugu Ishimoto, Keisuke Kosumi, Asuka Murata, Naoya Yoshida, Toru Beppu, Hideo Baba. Clinical, pathological and prognostic value of LINE-1 methylation in hepatocellular carcinoma. [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 1357. doi:10.1158/1538-7445.AM2014-1357