Genetic And Epigenetic Study On Cancer Related Genes In Relation To Esophageal Squamous Cell Carcinoma

[Objective] This study aims to investigate the role of exogenous factors, genetic polymorphisms, aberrant CpG island methylation of P16,MGMT and hMLH1 genes and their relations in the risk of esophageal squamous cell carcinoma in a Chinese population.[Methods]A population-based case-control study was conducted in Yangzhong County, Jiangsu Province of China, with histologically confirmed esophageal squamous cell carcinoma cases who were diagnosed between January 2004 and March 2006 while controls were selected from the local cancer-free individuals and group matched with cases by sex and age. Face-to-face interviews were conducted by the trained interviewers using a structured questionnaire and blood samples were collected with informed consent. For those patients having undergone surgery in the Yangzhong People's Hospital, tissues in the center of cancer focus and distant normal appearing esophagus were excised and stored in-70℃refrigerator. Ten histologically confirmed normal esophageal tissues from those who underwent gastroscopy examination were obtained in the Yangzhong People's Hospital. Polymerase Chain Reaction (PCR) and Restriction Fragment Length Polymorphism (RFLP) methods were used to measure DNA damage repair gene XPC and folate metabolism enzyme gene MTHFR polymorphisms. Unconditional logistic regression model was used to measure the relationship between exogenous factors and genetic polymorphisms and the possible gene-environment interaction in the risk of esophageal cancer. Methylation Specific Polymerase Chain Reaction (MSP) was used to test the CpG island methylation status of cancer related genes P16, MGMT and hMLH1．The assocoation between methylation status of selected genes and clinical characteristics as well as the possible interaction between methyaltion status and MTHFR C677T polymorphisms were also analyzed.[Results]Totally, 355 cases (men 62．8%, women 37．2%) were involved in this study with average age 61．5±7．9 years old, and group matched by 408 controls (men 61．8%, women 38．2%) with average age 60．8±8．3 years old. Stratified unconditional logistic regression analysis by sex showed that hot-temperature food items, pork braised in brown sauce and old stocked rice intake could increase the risk of esophageal cancer with odds ratio 2．13(95% confidence interval: 1．39-3．24),2．06(95% confidence interval: 1．42-2．99) and 9．06(95% confidence interval:5．93-13．84) in men and with odds ratio 3．05(95% confidence interval: 1．73-5．36) , 1．91(95% confidence interval: 1．16-3．16) and 14．53(95% confidence interval:7．82-27．02) in women respectively. Diet high in salt and chili only showed risk effects in men with odds ratio 2．34(95% confidence interval: 1．57-3．48) and 3．38(95% confidence interval:2．12-5．39) respectively. Either tobacco smoking or alcohol drinking showed risk effects in the occurrence of esophageal cancer for men with odds ratio 1．98(95% confidence interval: 1．34-2．92) and 2．20(95% confidence interval:1．51-3．20) respectively. Green tea drinking seemed to be a protective factor for women with odds ratio 0．26(95% confidence interval:0．07-0．94) . The frequency of H.pylori lgG seropositive in esophageal cancer cases was 55．0% which was lower than that in controls (62．6%). However, the difference was not significant.The frequency of allele XPC PAT+ and XPC exon 15C were 35．7% and 37．2% in cancer cases respectively. Compared with XPC PAT-/-genotype, the adjusted odds ratio for +/-and +/+ were 0．80(95% Cl:0．56-1．16) and 1．04(95% Cl:0．60-1．80) respectively. Compared with XPC exon 15 AA genotype, the adjusted odds ratio for AC and CC were 0．79(95% Cl:0．55-1．14) and 1．03(95% Cl:0．59-1．78) respectively. No significant relation was found between XPC polymorphisms and esophageal cancer.The frequency of allele MTHFR 677T were 45．6% and 45．3% in cases and controls respectively. After adjusted by sex, age, education years, tobacco smoking, alcohol drinking, green tea drinking and old stocked rice intake, the odds ratio for MTHFR CT and TT were 1．58(95% Cl:1．06-2．36) and 1．04(95% Cl:0．64-1．68) when compared with MTHFR CC genotype. No interaction was found between MTHFR C677T genetic polymorphisms and selected environmental factors.Aberrant CpG island hypermethylation of P16, MGMT and hMLH1 gene could be found in most cancer tissues with the frequency about 88．0%, 27．2% and 3．2% respectively, whereas the frequency of CpG island hypermethylation in any gene was 90．4%. Even in adjacent normal appearing esophageal tissues, the P16 and MGMT gene also showed high aberrant hypermethylation with the proportion at 36．8% and 11．2% respectively. Compared to those patients without lymph node metastasis, MGMT gene showed a higher proportion of hypermethylation in cancer tissues while P16 gene showed a higher proportion of hypermethylation in adjacent normal appearing esophageal tissues in patients with lymph node metastasis. A significant relation was found in this study between MTHFR C677T genetic polymorphisms and CpG island methylation status of MGMT gene in tumor tissues.[Conclusions]Both exogenous factors and genetic factors might play important roles in the occurrence of esophageal squamous cell carcinoma. A healthy dietary habit, with smoking cessation and alcohol controlling is of a great importance in the prevention of esophageal cancer. MTHFR C677T genetic polymorphisms were associated with individual susceptibility to esophageal cancer and hypermethylation rate of MGMT gene in the tumor tissues. Aberrant CpG island hypermethylation of cancer related genes were strongly related with esophageal squmaous cell carcinoma and could be a promising biomarker in esophageal cancer diagnosis and prognosis.