Folate Intake And Polymorphisms In Folate Metabolic Enzyme Genes In Association With Endometrial Cancer Risk And Prognosis

[BACKGROUND]Endometrial cancer,one of the most common gynecologic malignant tumors, usually occurs in the middle and elderly aged women.Reducing incidence and mortality of endometrial cancer,thus,has significant public health implication in women.Due to the important role of folate in production of nucleuids,the nutrient may have duel effect in carcinogenesis and progression of endometrial cancer,namely,high folate intake may decrease the risk of endometrial cancer by preventing the mutation of normal cells,but may stimulate the growth of pre-cancerous lesions or existing tumors.5,10-methylenetetrahydrofolate reductase(MTHFR) and thymidylate synthase (TYMS) are key enzymes in folate metabolism.Activities of the two enzymes have been suggested to affect serum levels of folic acid and homocysteine and predispose individuals to cancer susceptibility and chemotherapy sensitivity.Therefore,genetic variants in MTHFR and TYMS genes,which may alter the activities of MTHFR and TYMS,may be involved in the etiology and progression of endometrial cancer.[OBJECTIVES]To evaluate the effect of folate intake and polymorphisms of folate metabolic enzyme genes in the development and progression of endometrial cancer among Chinese women in Shanghai.Specifically,1.To investigate the independent and joint effects of dietary folate intake and genetic polymorphisms of MTHFR and TYMS genes on endometrial cancer risk in a population-based case-control study-the Shanghai Endometrial Cancer Study(SECS).2.To evaluate the role of dietary folate intake,vitamin supplement use and polymorphisms of MTHFR and TYMS genes in the progression of endometrial cancer by using data collected in the Shanghai Endometrial Cancer Follow-up Survey (SECFS).[METHODS]During 1997 to 2003,1,204 newly diagnosed endometrial cancer cases and 1,212 controls were recruited from women between the ages of 30 and 69 in urban Shanghai, China.Dietary intakes of folate and other methyl-related nutrients,including riboflavin (vitamin B2),vitamin B6,vitamin B12,and methionine,were derived from a validated food frequency questionnaire(FFQ).Use of vitamin supplement was also obtained through in-person interview using a structured questionnaire.Genotyping was performed on 1,041 cases and 1,030 controls for MTHFR 677C＞T(rs1801133), 1298A＞C(rs1801131) and 1793G＞A(rs2274976) and on 1,037 cases and 1,018 controls for htSNPs located in the TYMS gene or within the 5 kb region flanking the gene(rs502396,rs2244500,rs3786362,rs2853532,rs3744962,rs11081251,rs9948583, rs3819102,rs10502289,rs2298583 and rs2298581).Haplotype estimation of the SNPs was performed using Phase software.Odds ratios(ORs) and 95%confidence intervals (CIs) were calculated to evaluate associations of nutrients and genotypes with endometrial cancer.Associations of haplotypes with the cancer and possible interactions between haplotypes and environmental exposure factors in endometrial cancer were analyzed using HapSTAT software.1,454 endometrial cancer patients were followed-up with a combination of active survey and record linkage to the death certificates kept by the Vital Statistics Unit of the Shanghai Center for Disease Control and Prevention.Of the 1,204 patients included in the original study,1,032(85.7%) were successfully contacted from January to March, 2007 and information on vitamin supplement use and outcome of these patients was obtained.In April 2007,a record linkage with Shanghai Resident Vital Registry was operated for all 1,454 endometrial cancer cases in order to obtain or confirm the information of date of death and cause of death.The Kaplan-Meier method was used to compute 5-year survival rates and the log-rank test was applied to test the differences in survival across different groups.The multivariate Cox proportional hazards regression model was applied to evaluate the effect of dietary folate intake,vitamin supplement use,MTHFR or TYMS genotypes and haplotypes on overall survival and disease-free survival with adjustment for age and known prognostic factors for endometrial cancer. [RESULTS]In SECS,a significant inverse association between dietary folate intake and endometrial cancer risk was observed among all subjects and non-B vitamin supplement users.The greatest reduction in endometrial cancer risk was observed among non-B vitamin supplement users in the highest quartile of dietary folate intake (OR=0.5,95%CI:0.4-0.7) as compared with those in the lowest quartile.Dietary intake of folate cofactors(methionine,riboflavin,vitamin B6,and vitamin B12) was not related to the risk of endometrial cancer.Use of any vitamin supplement decreased 30%risk of endometrial cancer,and the risk decreased with increasing dose and period of use(P for trend＜0.01).Compared to non-supplement users,use of only B vitamins was inversely associated with the risk of endometrial cancer(OR=0.3,95%CI:0.1-0.8). No association was observed between endometrial cancer and the MTHFR 677C＞T, 1298 A＞C,and 1793G＞A polymorphisms.Among non- B vitamin supplement users, however,the 1298C and the 1793A alleles were associated with a lower risk of endometrial cancer among women with high dietary folate intake,but related to a higher risk among those with low dietary folate intake(P for interactions were 0.08 and 0.03,respectively).Further analysis observed a lowest risk(OR=0.6,95%CI:0.4-1.1) among women with the 1298C allele and highest intakes of both folate and riboflavin and a highest risk(OR=2.2,95%CI:0.9-5.7) among 1298C allele carriers with highest intake of folate but lowest intake of riboflavin(P for interaction=0.04).A similar association was observed for the 1793A allele(P for interaction=0.03).Of eleven TYMS htSNPs identified,polymorphism of rs3819102 in the 3'flanking region of the TYMS gene was associated with the risk of endometrial cancer.Compared with the TT genotype at SNP rs3819102,genotype CC was associated with increased risk of endometrial cancer(OR=1.5,95%CI=1.0-2.2),particularly among postmenopausal women(OR=1.7,95%CI=1.1-2.8).Haplotype TTG at block 2 of TYMS gene,which included three htSNPs in the 3' flanking region,rs10502289,rs2298583 and rs2298581, was inversely associated with the risk of endometrial cancer under dominant(OR=0.8, 95%CI=0.6-1.0) and additive(OR=0.8,95%CI=0.7-1.0) but not recessive(OR=1.2, 95%CI=0.4-3.9) models.A significant multiplicative interaction was found for TYMS haplotypes at block 2 with postmenopausal status in endometrial cancer risk(P for interaction=0.0008). In SECFS,the median follow-up time for 1,454 endometrial cancer cases was 5.2 years after cancer diagnosis by the end of 2006.Overall 5-year survival rate of 86.31% and 5-year disease-fiee survival rate of 90.78%were observed for the case cohort.The important clinically prognostic factors of endometrial cancer in this population included pathological type and stage,cancer cell differentiation and status of estrogen receptor (ER) and progesterone receptor(PGR).Age,education level and postmenopausal status were also associated with endometrial cancer survival.While no association was observed for folate intake,MTHFR and TYMS genetic polymorphisms with endometrial cancer survival,a significant increased risk of endometrial cancer death was observed for MTHFR haplotype ACC under recessive model,with age-adjusted hazard ratio(HR) being 4.36(95%CI:1.07-17.76).Further adjusting for the known prognostic factors mentioned above strengthened the association(HR=7.95,95%CI:1.78-35.49).Use of any vitamin supplement after diagnosis was observed to decrease the risk of endometrial cancer death.The protective effect,however,was due to survival bias.[CONCLUSION]Our findings suggest that dietary folate intake may decrease the risk of endometrial cancer,but has no effect on endometrial cancer survival;use of vitamin supplement decreases the risk of endometrial cancer and is not detrimental to the prognosis of the disease;while MTHFR genetic variants have no main effect in the development and progression of endometrial cancer,MTHFR polymorphisms modify the effect of folate intake on the risk of endometrial cancer and MTHFR haplotypes are associated with endometrial cancer survival;TYMS polymorphisms and haplotypes may affect or modify the risk of endometrial cancer.