Abstract 686: LINE-1 %5-Methylcytosine levels in pre-diagnostic leukocyte DNA and subsequent renal cell cancer risk .
Authors: Karami Sara , Andreotti Gabriella , Pfeiffer Ruth M. , Liao Linda M. , Weinstein Stephanie , Albanes Demetrius , Virtamo Jarmo , Rothman Nathaniel , Moore Lee E. 
Published: August 2014

Background: Alteration of DNA methylation is thought to promote carcinogenesis by weakening chromosomal stability and changing normal gene expression patterns. These epigenetic alterations that occur throughout the genome are considered early events in the carcinogenic process. Lately, long interspersed nucleotide element (LINE-1) methylation levels in blood DNA have been examined in relation to risk of several cancers. One previous renal cell cancer (RCC) case-control study reported higher LINE-1 methylation levels in blood DNA for cases than controls. Since DNA samples from that study were collected post-diagnostically, it remains unclear if the observed difference occurred prior to, or as a result of carcinogenesis. Thus, we examined the association between global methylation and RCC risk using prospectively collected blood samples.

Methods: A nested RCC case-control study was conducted amid subjects in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) cohort, a study of Finnish male Caucasian smokers, 50 to 69 years old. LINE-1 percent 5-methylcytosine (LINE-1 %5-MeC) levels from 191 cases and 575 controls, matched on age at randomization (+/-5 years), were quantified using bisulfite treated blood DNA and pyrosequencing. Cancer risk was assessed in quartiles (Q1:&lt;78.0, Q2:78.0-78.5, Q3:78.6-79.5, Q4:&gt;79.5) of methylation based on control levels. Unconditional logistic regression was used to compute odds ratios (ORs) and 95% confidence intervals (CIs) adjusting for pack-years of smoking, age at randomization, hypertension, family history of cancer, body mass index (BMI) and intervention group.

Results: RCC risk was significantly increased with increasing LINE-1 %5-MeC levels (Q1REF. vs. Q2OR= 1.12 (0.63-1.92), Q3OR= 1.78 (1.06-3.00), Q4OR= 1.78 (1.00-3.03); p-trend= 0.01). Associations appeared more pronounced for males with a higher BMI: (BMI &lt;25kg/m2: Q1 vs. Q2-Q4OR= 0.89 (0.35-2.23); BMI 25-&lt;30kg/m2: Q1 vs. Q2-Q4OR= 1.21 (0.67-2.17); BMI ≥30kg/m2: Q1 vs. Q2-Q4OR= 8.86 (2.20-35.68); p-interaction= 0.01). Decreasing LINE-1 %5-MeC levels were observed with increasing BMI for controls (p-trend= 0.004) but not cases (p-trend=0.19). Analyses for pack-years of smoking showed no association with LINE-1 %5-MeC levels in cases or controls; pack-years of smoking was not shown to modify associations.

Conclusion: Our study findings that increasing LINE-1 %5-MeC levels were associated with higher RCC risk using pre-diagnostically collected blood DNA are consistent with results reported in a previous case-control study. Yet, stratified results for BMI and smoking observed post-diagnostically in that case-control study are not supported in pre-diagnostic samples used here. Our results suggest that higher methylation levels are reflective of elevated RCC risk prior to diagnosis. Additional studies are being conducted in a second cohort to replicate these findings.

Citation Format: Sara Karami, Gabriella Andreotti, Ruth M. Pfeiffer, Linda M. Liao, Stephanie Weinstein, Demetrius Albanes, Jarmo Virtamo, Nathaniel Rothman, Lee E. Moore. LINE-1 %5-Methylcytosine levels in pre-diagnostic leukocyte DNA and subsequent renal cell cancer risk . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 686. doi:10.1158/1538-7445.AM2013-686