PREDICTION OF TOBACCO EXPOSURE IN LUNG CANCER PATIENTS EMPLOYING DDPCR ASSAY METHYLATION-BASED AND MUTATIONAL SIGNATURE

Introduction: Mutational signatures reflect the mutational processes in malignant cells and provide information about environment exposure. Environment exposure is also highly associated with epigenetics events and the level of DNA methylation. Recently, methylation of AHRR gene (cg05575921) was reported decreased in smokers, also allowing to inferred the tobacco exposure, which is the major etiologic factor of lung cancer. Aim: To associate mutational signature and smoking-associated methylation levels in lung cancer patients. Methodology: We evaluated paired blood and tumor samples from non-small cell lung cancer (NSCLC) patients (n=40) categorized as never (n=4), former (<=15y:n=6/>15y:n=11) and current (n=18) smokers. Whole-exome sequencing was performed in fresh-frozen tumor tissue by Illumina HiSeq2500. Mutational signatures were determined by Somatic Signatures and the nucleotide substitution (C>A) related with tobacco exposure (Signature 4) was categorized (<25%, 25-50%, >50%). The methylation levels of cg05575921 in blood was determined by methylation-based ddPCR assay. Results: The methylation levels of cg05575921 ranged from 21.388.4%. Former/current smokers presented decreased methylation levels of cg05575921 compared with never smokers (p<0.0001). Decreased methylation levels of cg05575921 was associated with higher C>A substitution (>25%;p=0.03). Number of pack/years did not correlated with methylation levels of cg05575921 (p=0.3;r=-0.2). Conclusion: Mutational signatures are profitable for evaluation of tobacco exposure and correlated with AHRR methylation levels. Assessment of tobacco exposure through the ddPCR in minimally invasive samples is feasible and can be clinically implementable to confirm smoking habits in NSCLC patients besides it can be a valuable tool for retrospective studies enrolling tobacco exposure.