Abstract 4337: Identifying epigenetic biomarkers in a clinical cohort of individuals with oropharyngeal cancer
Authors: Langdon Ryan 
Published: August 2019

Abstract
Oropharyngeal cancer (OPC) shows a distinct epidemiology to other head and neck cancer (HNC) subtypes. Several lifestyle and dietary factors as well as viral infections have been implicated in altering both incidence and prognosisfor OPC, notably smoking, alcohol consumption and HPV infection. We aimed to: 1) assess the impact of these epidemiological factors on epigenome-wide DNA methylation patterns, 2) evaluate whether DNA methylation patterns were associated with survival from OPC,3) ascertain whether novel exposure or prognostic indicators could be derived from DNA methylation patterns and 4)establish whether DNA methylation plays a causal role in mediating the impact of prognostic factors on survival.In a large prospective HNC cohort (Head and Neck 5000) we undertook epigenome-wide association study (EWAS) and differentially-methylated region (DMR) analyses of the aforementioned prognostic factors and mortality, using methylation data on &gt;850.000 CpG sites measured using theIllumina MethylationEPIC on 420 individuals diagnosed with OPC . We performed multivariable linear regression analysis of DNA methylation against the prognostic factors, and Cox regression analysis of survival in relation to DNA methylation. We then determined the extent to which any results mediated the pathway between prognostic factors and OPC mortality using Mendelian randomization (MR).We identified CpG sites and DMRs associated with smoking and alcohol consumption below our multiple-testing threshold, but none with HPV positivity. We also identified 7 CpGs associated with survival (~3 years post-diagnosis), independent of smoking, alcohol consumption and HPV positivity. 18 CpGs across 3 DMRs were found to be associated with both smoking and mortality and 5 CpGswithin 1 DMR were identified in relation to both alcohol and mortality. We hypothesised that for these CpG sites there could be a mediating effect of DNA methylation, whereby DNA methylation mediates the association between the prognostic factor and OPC mortality. Using an inverse-variance weighted (IVW) MR approachto investigate the causal effect of DNA methylation at the identified sites, we found that hypomethylation in CpGslocated within a DMR associated with smoking (Chr2:220325443-220326041; annotating to the SPEG gene) showed some evidence of a causal effect on increased mortality (HR: 1.15, 95% CI: 1.05 to 1.25, P: 1.12x10-3). Within the context of OPC, we found novel epigenetic biomarkers measured by the Illumina MethylationEPIC array to be associated with the prognostic factors of smoking and alcohol, and with mortality, respectively. We also found preliminary evidence of a potential mediating effect of DNA methylation at the SPEG gene, between smoking and OPC mortality. However, longer follow up in Head and Neck 5000 and suitable replication data is needed to strengthen the validity of these findings.
Citation Format: Ryan Langdon. Identifying epigenetic biomarkers in a clinical cohort of individuals with oropharyngeal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4337.