MA06.07 Genetic and Epigenetic Alterations are Associated with Tumor Mutation Burden in Non-Small Cell Lung Cancer

Abstract

Although several studies have indicated that tumor mutation burden (TMB) is associated with non-small cell lung cancer (NSCLC) development and clinical efficacy of immune checkpoint inhibitors (CPIs), identification of factors associated with TMB is still a major biological issue. It is well-known that DNA transcription can be regulated through methylation and demethylation, gene silencing caused by DNA hypermethylation is associated with cancer development. However, the relationship between DNA methylation and TMB in NSCLCs remains unclear. The landscape of DNA sequence in Chinese NSCLCs population were surveyed by using whole-exome sequencing (WES) by profiling 178 lung tissues (89 without any systemic anti-cancer therapy tumors and matched normal lung tissues). According to the 104 median-level of TMB in our cohort, high TMB (n=16, 252-465 range mutations per tumor) and low TMB (n=13, 57-79 range mutations per tumor) groups were divded. The NSCLC methylome between high and low TMB was characterized on a genome-wide scale using Illumina Infinium MethylationEPIC arrays combined with the WES data. The results show frequently aberrant DNA methylation, abundant chromosomal amplifications and deletions, and mutational signatures in high TMB lung cancer. Combining with clinical data, cigarette smoking associated with high TMB were observed in our cohort. Cancer-specific epigenetic alterations were observed in 294,141 CpG sites, comprising both tumor hyper- (769,38) and hypo- (217,203) methylation in high TMB lung cancer while none in low. These different methylations sites cover 1232 genes including 25 HOX genes. Global DNA hypomethylation and TP53 mutation, associated with increased chromosomal instability, were associated with TMB in NSCLCs.The high TMB NSCLCs are characterized by numerous copy number alterations and aberrantly methylated sites and display distinct mutational signatures. 25 hypermethylated HOX genes can be potentially useful as DNA methylation markers for prediction of TMB level. The results provide insights into the epigenetic impact of TMB, which may contribute to improve precison management of NSCLCs.