Expression And Clinical Significance Of O~6-Methylguanine DNA Methyltransferase In Esophageal Carcinoma

IntroductionEsophageal carcinoma is one of the most common malignant cancer in our country.Now surgery and radiation therapy are the effective methods.The five-year survival rate of early esophageal carcinoma is more than 90%after surgical treatment.However,the five-year survival rate for middle and advanced stages patients is less than 10%.Chemotherapy was used in adjuvant therapy after surgical treatment,and the effect of single drug is very poor.Effect of combining chemotherapy has been improved than single drug.whereas,status in quo chemotherapy has not been satisfied.Resistance of anti-cancer drugs is responsible for chemotherapy failure of tumors.O~6-Methylguanine-DNA Methyltransferase(MGMT) is a protein related with resistance of anti-cancer drugs.Alkylating agent is a revulsant and carcinogen in environment.It can induce the form of alkyl adduct in DNA-O~6 position, O~6-Methylguanine(O~6-MG) is a primary adduct.The DNA injure could induce activation of oncogene and inactivation of tumor suppressor gene easily which come into tumor,if the injure can not be repaired in time.MGMT is responsibility for this kind of DNA repair,consequently guanine can be repaired,and MGMT lost activity inreversibly due to obtaining the alkyl.So MGMT play a important role in cell protecting for avoiding alkyl injure and preventing cell cancerization and death.Expression of MGMT is more higher in liver,lymph node and intestines in normal tissue,and less lower in lung and brain relatively.Expression of MGMT is more higher in most tumor tissue than corresponding normal tissue.Studies at present have show that MGMT is associated greatly with carcinogenesis,progression,biologic behavior and tumor resistant.Some factor,for example mutation of MGMT gene,genetic polymorphism and promoter hypermethylation,can affected structure and expression of gene and expression of protein which would lead to cancerization.Resistance of anti-cancer drugs is a very familiar phenomenon in alkylating agent chemotherapy,and that the phenomenon is related with content of MGMT protein.Application of MGMT inhibitor and gene silence technique can reduce expression of MGMT,and improve sensitivity of tumor cell to alkylating agent.It can improve expression level of MGMT in cells and enhance endurance of normal tissue to alkylating agent,and reduce side effect of alkylating agent after mutant gene transfer of MGMT into normal histocyte.But the relationship between MGMT and clinic pathologic characteristics of esophageal carcinoma have been reported infrequencely.The aim of this study is to demonstrate the relationship between MGMT and pathologic characteristics of esophageal carcinoma by detecting the expression of MGMT in esophageal carcinoma and normal tissue by immunohistochemistry method.And the study would provide theoretics evidences for further explore in evaluating prognosis of esophageal carcinoma.Material and MethodsTumor sample were obtained from 57 patients with 43 males and 14 females, who underwent resection of esophageal carcinoma in hospital between Jan.2006 and Dec 2006.The range of ages were 41-78 years.The average ages were 58.8±8.8 years.Pathologic classify included 47 high or middle differentiation squamous cell carcinoma and 10 low differentiation squamous cell carcinoma.Local node metastasis was examined in 20 patients and nothing in 37 patients.Tumor invasion depth is submucosa in 7 patients,muscle segment in 16 patients and ectoblast in 34 patients.Clinical TNM classification is stageⅠor stageⅡin 41 patients,and stageⅢor stageⅣin 16 patients.Tumor was watched in super or middle segment of esophagus in 40 patients,and lower segment in 17 patients.20 normal esophageal tissue of chronic gastritis was obtained as control.All sample were fixed with 10%formalin and embedded with paraffin regularly,then sliced up continuously in 4μM thickness,and colorated respectively with HE coloration method and immunohistochemistry coloration method. Expression of MGMT in tumor tissue and normal tissue were detected.Determinant standard for result is that 5 high-time microscope views in each slice were choosed and 500 tumor cell were counted.1.Scoring according to positive cell rate:zero point is not more than 5%positive cell in nucleolus,one point is 6-49%positive cell in nucleolus,two point is not less than 50%positive cell in nucleolus.2.Scoring according to coloration degree:zero point is none coloration,one point is mild coloration,two point is strong coloration.The points of two item were added,0-1 point count negative and 2-4 point count positive. All data were analyzed statistically by SPSS13.0 statistic software,Pearson's x~2-test t were used in grouping difference of sex,age etc,and logistic regression analysis is used in multifactor analysis.P value less than 0.05 were considered as statistically significant.Results1,Expression of MGMT in normal and esophageal carcinoma tissueThe positive rate of MGMT in esophageal carcinoma tissue were 49.1%(28/57) and the positive rate of MGMT in normal esophagus mucosa were 85.0%(17/20), and the difference was statistic significant(x~2=7.744,P=0.005).2,The relation between expression of MGMT and clinic pathplic featureThe positive expression rate of MGMT was 51.2%(22/43) in male and 42.9% (6/14) in female,50.0%(18/36) in more than 60 years old patients and 47.6% (10/21) less than 60 years old patients,48.9%(23/47) in high or middle differentiation patients and 50.0%(5/10) in low differentiation,45.0%(18/40) in super or middle segment of esophagus and 58.8%(10/17) in lower segment,14.3 %(1/7) in submucosa,31.3%(5/16)in muscle and 64.7%(22/34)in ectoblast,39.0 %(16/41) in stageⅠorⅡand 75.0%(12/16) in stageⅢorⅣ,75.0%(15/20) in patients with local node metastasis and 35.1%(13/37) in patients without local node metastasis.The positive Expression of MGMT showed obvious grouping difference statistically in invade degree(x~2=8.594,P=0.014),tumor stage(x~2=5.855,P=0.016), local node metastasis(x~2=8.110,P=0.004),and none grouping difference statistically in sex(x~2=0.286,P=0.593),age(x~2=0.030,P=0.864),position(x~2=0.896,P=0.344), differentiated grade(x~2=0.004,P=0.952). Logistic regression analysis was used in filtrating correlated factor, age(P=0.257),sex(P=0.196),differentiated grade(P=0.197),position(P=0.401),invade degree(P=0.112),local node metastasis(P=0.206),tumor stage(P=0.679) were no correlation with expression of MGMT.Conclusion1,The positive rate of MGMT in esophageal carcinoma were less than that in normal esophagus mucosa.The results indicated that lack expression of MGMT may play a role in esophageal carcinoma tumorigenesis.2,Age,sex,differentiated grade,position,invade degree,local node metastasis,tumor stage were no correlation with expression of MGMT in esophageal carcinoma. The results indicated that MGMT can not be considered to be a independent factor for evaluating prognosis of esophageal carcinoma.