The Significance Of GSTP1 Gene Promoter Methylation In The Diagnosis Of Lung Cancer

Lung cancer is the most common and lethal malignancy in the world.Since the disease remains asymptomatic for a long time,most of the clinically diagnosed lung cancers patients present with advanced or metastatic stage,which implies a dismal prognosis,and the 5-year survival rate for lung cancers is less than15%.Early detection of lung cancer could improve the outcome of the disease.Imagiological diagnosis and cytologic examination are the predominant screening methods currently,and molecular marks also have granted appositive insurance decision on sreening.The role of DNA methylation in the development of lung cancer is a hot topic.DNA methylation is an important mechanism that control gene transcription in gene promoter and the first exon.Aberrant methylation has been associated with various malignant diseases.Glutathione S-transferase P1(GSTP1)belongs to a family of carcinogen II metabolizing enzymes that can protect cells from carcinogens and oxidative damage,and it plays an important role in the prevention of cancer.The role of GSTP1 gene methylation in the development of lung cancer is yet insufficiently explored.The detection of gene in tumor is often limited by biopsy tissue accessibility because of not suitable for surgeries and patients performance statue.Therefore,in this study,we investigated firstly whether bronchoalveolar lavage fluid(BALF)could substitute for tumor tissues for the detection of GSTP1 gene methylation.Then the association between GSTP1 gene promoter methylation among tumor markers(NSE?ProGRP?CAl25 and CYFRA21-1)and the relationship between GSTP1 gene promoter methylation and clinicopathological features of lung cancer also were analyzed.The purpose of the study was to assesse clinical value and significance of GSTP1 gene methylation in the diagnosis of lung cancer,and search for a diagnosis molecular markers for lung cancer.Methods1.Experimental groups:(1)Whether bronchoalveolar lavage fluid(BALF)could substitute for tumor tissues for the detection of GSTP1 gene methylation: BALF and the tissue samples of 50 patients with lung cancer were collected,they were alveolar lavage fluid group and lung cancer group,respectively.(2)The research on GSTP1 gene promoter methylation in the diagnosis of lung cancer: The lung cancer group was constituted by 100 lung cancer patients,and the control group contained 100 patients with benign lung diseases,their BALF and peripheral blood were collected,the healthy group included 100 peripheral blood specimens from healthy people.2.PCR and high resolution melting assay(PCR-HRM)was used to analyze GSTP1 gene methylation.Electrochemiluminescence was used to detect the levels of tumor markers NSE,ProGRP,CAl25 and CYFRA21-1.3.Data analysis: SPSS17.0 statistical software was applied for the data statistics.The methylation rates of GSTP1 gene was expressed with detection rates(%).whether bronchoalveolar lavage fluid(BALF)could substitute for tumor tissues for the detection of GSTP1 gene methylation was analyzed by Mc Nemar's test.Chi-square test was used to compare the methylation rates of GSTP1 gene in different groups.GSTP1 gene methylation and tumor makers were compared with kappa statistic.The diagnostic sensitivity and specificity was analyzed by receiver operating characteristic curves.Chi-square test also was used for analysis the relationship between GSTP1 gene methylation and clinical and pathological features.P < 0.05 was considered statistically significant.Results1.Whether bronchoalveolar lavage fluid(BALF)could substitute for tumor tissues for the detection of GSTP1 gene methylation: The methylation rates of GSTP1 gene promoter in the lung cancer tissue group and BALF group were 48.0%(24/50)and 44.0%(22/50),respectively,and there were no significant difference between the GSTP1 gene promoter methylation in BALF group and the tissue samples group(P=0.688).2.Detection of GSTP1 gene methylation status and its diagnostic sensitivity and specificity: The methylation rates of GSTP1 gene promoter in the lung cancer group and control group were 57.0%(57/100)and 12.0%(12/100),respectively.After ROC curve analysis,we found that the diagnostic value was best when the cut-off values of GSTP1 gene methylation was 5%,and its diagnostic sensitivity and specificity were 57.0% and 88.0%,respectively.And the methylation rate of the promoter of GSTP1 gene in the lung cancer group was 48.0%(48/100),which was significantly higher than that in the control group 11%(11/100),(?2=32.91,P<0.001).3.The value of promoter methylation of GSTP1 gene in the diagnosis of lung cancer: The kappa values between GSTP1 gene methylation and serum tumor markers(NSE?ProGRP?CAl25 and CYFRA21-1)were 0.733?0.712?0.466 and 0.485.With the ROC curve analysis,it shown that the AUC values of promoter methylation of GSTP1 gene in BALF and serum tumor markers(NSE?ProGRP?CAl25 and CYFRA21-1)were 0.719 ? 0.814 ? 0.839 ? 0.698 and 0.884.The diagnostic sensitivity of methylation of GSTP1 gene was lower than NSE,but its diagnostic specificity was the same as NSE.And its diagnostic sensitivity and specificity were both higher than CA125.3.Analysis of the association between GSTP1 gene promoter methylation and clinicopathological features of lung cancer: There were no significant correlations between the methylation status of GSTP1 gene and age,gender or pathological type of patients with lung cancer(P=0.414,P=0.628,P=0.101).The methylation rate of the promoter of GSTP1 gene in stage?and? patients with lung cancer was significantly lower than the stage ? and ? patients(?2 =11.422,P=0.001),but obviously higher than the control group(?2 =11.014,P=0.001).The methylation rate of the promoter of GSTP1 gene in well and moderately differentiated patients with lung cancer was significantly lower than poorly differentiated patients(?2 =6.615,P=0.010),but obviously higher than the control group(?2 =15.591,P<0.001).Conclusion1.Bronchoalveolar lavage fluid(BALF)could substitute for tumor tissues for the detection of GSTP1 gene methylation.2.The GSTP1 gene promoter of patients with lung cancer was high methylated state.Its diagnostic sensitivity and specificity were 57.0% and 88.0%,respectively,and the diagnostic value was good.It was consistent with tumor markers in the diagnosis of lung cancerit.It might be used for the diagnosis of lung cancer.3.GSTP1 gene promoter methylation was associated with lung cancer pathological staging and differentiation degree.