Lung cancer remains a global health problem with a high mortality rate. CpG island methylation is a common aber-ration frequently associated with gene silencing in multiple tumor types, emerging as a highly promising biomarker. The transmembrane protein with a single EGF-like and two follistatin domains (TMEFF2) is epige-netically silenced in numerous tumor types, suggesting a potential role as a potential tumor suppressor. However, the role of TMEFF2 in lung cancer remains to be fully elucidated. We explored the methylation status of TMEFF2 gene in 139 patients with non-small cell lung cancer (NSCLC) and the feasibility of detecting circulating methylated DNA as a screening tool for NSCLC using methylation-specific PCR in 316 patients and 50 age-matched health controls. TMEFF2 methy-lation in tumor tissues was found in 73 of the 139 NSCLCs (52.5%) and was related to gene expression. The frequency of TMEFF2 methylation was higher in females and never-smokers than in males and smokers with borderline significance (65.8% vs 47.8%, p = 0.06; 65.7% vs 48.1%, p = 0.07). Notably, in adenocarcinomas, TMEFF2 methylation was significantly more frequent in tumors without EGFR mutation than those with EGFR mutation (adjusted odds ratio = 7.13, 95% confidence interval = 2.05-24.83, P = 0.002). Furthermore, TMEFF2 methylation was exclusively detec-ted in the serum of NSCLC patients at a frequency of 9.2% (29/316). These findings suggest that methylation-asso-ciated down-regulation of TMEFF2 gene may be involved in lung tu-morigenesis and TMEFF2 methylation can serve as a specific blood-based biomarker for NSCLC.

Keywords: methylation, methylation-specific PCR, non-small cell lung cancer, serum, TMEFF2