Abstract 1265: The effects of ancestry and histology on the lung tumor methylome
Authors: Rossi Emily L. , Zhao Isaac , Arauz Rony F. , Zingone Adriana , Ryan Bríd M. 
Published: September 2020

Methylation-based biomarkers can provide molecular insight on the contribution of ancestry and histology to lung tumor biology. Loss of global methylation is a benchmark of aging and a signal of declining biological maintenance. In addition to aging, global loss of methylation occurs in response to some cancer-promoting exposures, including tobacco use. Reduced levels of global DNA methylation are associated with increased risk of several cancers, including lung. In lung tumors, global DNA hypomethylation is often associated with a more aggressive diseases and shorter survival time.

Several studies have identified population-level differences in global methylation present at birth. Additionally, gender and ancestry influence DNA methylation age (DNAm) and may predispose some individuals to accelerated aging. We hypothesized that differences in global hypomethylation and accelerated aging may contribute to differences in lung tumor biology by genetic ancestry. Therefore, we investigated methylome differences between European Americans (EA) and African Americans (AA) from the NCI-Maryland Case Control Study, which is overrepresented with AA patients (~40%) from the Baltimore area. We assessed lung tumor and paired non-involved adjacent tissue (NAT) methylation (n = 77 EA, n = 39 AA) using the Illumina EPIC methylation array. We used the Repetitive Element Methylation Prediction (REMP) package in R to identify roughly 20,000 predicted LINE-1 CpG's. We observed significantly decreased LINE-1 methylation in tumor tissue compared with NAT in both AA and EA. Additionally, among tumor samples we observed significantly decreased LINE-1 methylation in AA LUSC samples compared to EA LUSC, with only modest differences between AA LUAD and EA LUAD. In addition to decreased levels, LINE-1 methylation in AA LUSC tumors also had the greatest heterogeneity within CpG's of the same sample and between other AA LUSC samples. We observed accelerated aging (increased DNAm relative to chronological age) in 57/67 EA NAT samples and 28/38 AA NAT samples with no significant differences in age acceleration between ancestry or histology.

Our results show global hypomethylation of LINE-1 is a distinctive feature of LUSC in AA compared to EA, which is consistent with the enhanced genomic instability observed in AA LUSC relative to EA LUSC. We also observed accelerated aging in the vast majority of the NAT samples, which may implicate accelerated age with lung cancer risk. Future analysis will work towards completing a comprehensive analysis of the epigenetic landscape of lung cancer in AA and EA patients. We plan to study the relationship between global hypomethylation and genetic variants, smoking behaviors, and patient survival.

Citation Format: Emily L. Rossi, Isaac Zhao, Rony F. Arauz, Adriana Zingone, Bríd M. Ryan. The effects of ancestry and histology on the lung tumor methylome [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1265.