Epigenetic analysis of microRNA genes in tumors from surgically resected lung cancer patients and association with survival

Aberrant microRNA (miRNA) expression is involved in tumorigenesis of several cancers, including non-small cell lung cancer (NSCLC). Furthermore, expression of some miRNAs has been shown to be under epigenetic regulation. However, less is known regarding the role of miRNA methylation in NSCLC development or clinical outcomes. Therefore, we tested miRNA methylation patterns by quantitative real-time methylation-specific PCR for a panel of candidate miRNAs in 19 NSCLC paired tumor and adjacent normal tissues. For assessment of survival, methylation was measured in a total of 97 tumor tissues with complete clinical and follow-up data. Analysis was also performed for correlation with age at diagnosis, gender, smoking, and stage. Significant differences in methylation patterns were observed for 9 of the 12 miRNAs, all due to hypermethylation in the tumor tissue. Individuals with the highest levels of methylated miR-127 were at a significantly increased risk of dying with a hazard ratio of 1.93 (95% CI 1.17-3.19; P=0.010), in univariate analysis and remained significant after adjusting for age, gender, and stage (HR 1.97; 95% CI 1.15-3.40; P=0.014). This increase in risk due to increased methylation were accompanied by significant, dramatic difference in survival duration of 17 months (P=0.0089). Six of the 12 miRNAs were significantly positively correlated with age at diagnosis. Additionally, methylation of miR-127 was significantly greater in higher stage tumors compared to lower stage tumors (P=0.0039). However, no significant associations between smoking and gender with miRNA methylation were observed. Our results demonstrate that miRNA methylation plays a role in NSCLC tumorigenesis and prognosis.