Inactivation of the p16 and ESR1 tumor suppressor genes by promoter lesion methylation has been reported in many tumor types, including lung cancer. We examined the blood of 95 non-small cell lung cancer patients (66 cases of adenocarcinoma, 23 of squamous cell carcinoma and 6 of large cell carcinoma) and 30 controls consisting of normal subjects and benign disease patients to determine the methylation ratios of p16 and ESR1 using real-time PCR. For both genes, there was a statistically significant difference in the methylation ratio between non-small cell lung cancer patients and controls (p16; p<0.01, ESR1; p<0.001). In addition, there was a strong correlation between the methylation ratio of each gene and old age (p16; p<0.01, ESR1; p<0.001 and p16 or ESR1; p<0.001), and between p16 or ESR1 methylation rate and smoking history (p<0.01). Moreover in Stage I cases, the methylation positive rate of each gene (p16, ESR1 and p16 or ESR1) was higher than the CEA positive rate (p<0.05, p<0.001, p<0.001). Evaluation of p16 and ESR1 promoter methylation in blood using real-time PCR appears to be very useful for lung cancer diagnosis and there is some possibility that these methylated genes might come to represent useful biomarkers for the early detection of lung cancer. Our study results also suggested that comparative evaluation of the methylation ratio before and after surgery might be a powerful tool to predict the prognosis of lung cancer patients.

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