Hypomethylation of RPTOR in peripheral blood is associated with very early-stage lung cancer.

PURPOSE:Lung cancer (LC) is the leading cause of cancer-related deaths worldwide. Novel biomarkers for LC detection are urgently needed. Here we aimed to investigate the association between RPTOR methylation in peripheral blood and LC. METHODS:The methylation levels were measured by mass spectrometry in two independent case-control studies (159 LC cases vs. 188 controls in Study I, 413 LC cases vs. 687 controls in Study II). Logistic regression and Bonferroni correction were conducted to analyze the association. RESULTS:RPTOR hypomethylation was discovered in Study I and validated in Study II. Combining the two studies, RPTOR_CpG_2 and RPTOR_CpG_8 showed significantly lower methylation levels in stage I cases (ORs per -10% methylation = 1.22 and 1.27, respectively, both P-values < 0.005). The significance kept between RPTOR_CpG_8 and LC cases with tumor length ≤ 1 cm (OR per -10% methylation = 1.39, P = 0.001). Moreover, methylation levels of all CpG sites were lower in cases at stage II & III than in those at stage I (all P-values less than 0.017). CONCLUSION:Our study disclosed the association between RPTOR hypomethylation in peripheral blood and LC even in very early stage, suggesting the feasibility of blood-based DNA methylation for LC early detection.