Methylenetetrahydrofolate reductase polymorphisms and interaction with smoking and alcohol consumption in lung cancer risk: a case-control study in a Japanese population

The protective effects of the methylenetetrahydrofolate reductase rs1801131 variant among Saudi smokers

Methylenetetrahydrofolate reductase (MTHFR) polymorphism plays a fundamental role in susceptibility to various diseases, including cancers and autoimmune diseases. In the current study, we aimed to compare genotype and allele frequency variations of rs1801131, one of the most common variants found in the MTHFR gene, among Saudi smokers and non-smokers. We hypothesized that genetic variations of this gene are responsible for many diseases, particularly those caused by cigarette smoking (CS) such as pulmonary diseases, oral cancer and lung cancer. We performed a case-control study on a sample of 235 healthy smokers and 239 healthy non-smokers in Saudi Arabia. The rs1801131 SNP genotypes were determined using a genotyping assay and multiple in silico algorithmic software programs were used to identify the effects and structural functions of the rs1801131 (Glu429Ala) mutation. Using chi-squared tests, we found that, among smokers, TG and GG genotype carriers had 0.209-fold (OR = 0.209, P < 0.005) and 0.427-fold (OR = 0.427, P = 0.003) lower risks of CS-related disease compared to TT reference genotypes. In addition, this protective effect was observed in Saudi smokers independent of age, gender, types of smoking, duration, and average daily smoking consumption. Filling a research gap by exploring this topic in the Saudi population, the current findings indicate that genotype and allele distributions of MTHFR rs1801131 polymorphism present fundamental protective effects against the risk of CS-related disease. These findings should be verified in future studies with larger sample sizes, different ethnicities, and patients suffering from CS-related diseases, such as oral cancer and lung cancer.

Folate/homocysteine metabolism and lung cancer risk among smokers

Background

Folate and homocysteine are involved in DNA synthesis and methylation processes, which are deregulated during carcinogenesis.

Objectives

The aim of this study was to assess the relationship between folate/homocysteine concentrations, the functional polymorphisms of folate/homocysteine genes and lung cancer risk among cigarette smokers.

Study design

The study included 132 lung cancer patients and 396 controls from northern Poland, matched by sex, age and smoking status. The median cigarette pack-years of smoking among both cases and controls was 30.0. Serum, red blood cell (RBC) folates and serum homocysteine concentrations were measured. The genotypes in selected polymorphic sites of the MTHFR, CBS, SHMT1, MTHFD1, MTRR, MTR, TYMS DHFR, TCN2, and SLC19A1 genes were determined. All study participants underwent scanning with low-dose computed tomography.

Results

Serum folate concentrations above the median (> 17.5 nmol/l among the healthy controls) were associated with an increased lung cancer risk (odds ratio [OR], 1.54, 95% confidence intervals [CI], 1.04–2.29, P = 0.031). An analogous trend was observed when the population was analysed after subdivision according to RBC folate concentrations, that is, above a value of 506.5 nmol/l (OR, 1.53; 95% CI, 0.95–2.47; P = 0.084). Additionally, in a subset of women, an increased risk of lung cancer development was associated with the SLC19A1 c.80AA genotype (c.80AA versus GG OR, 3.14; 95% CI, 1.32–7.46; P = P = 0.010).

Conclusion

These results suggest that, in the population consisting of heavy smokers, high folate levels add to the cancerogenic effect of smoking.

Interaction between alcohol consumption and methylenetetrahydrofolate reductase polymorphisms in thyroid cancer risk: National Cancer Center cohort in Korea

The effect of alcohol intake on thyroid cancer is unestablished, and its interaction effects with genetic susceptibility are unclear. In this case-control study, the relationship among alcohol intake, the methylenetetrahydrofolate reductase (MTHFR) gene, and thyroid cancer risk has been evaluated. In total, 642 cases and 642 controls of Korean origin were included, and the genetic variants C677T and A1298C of the MTHFR gene were analysed. The interactions between alcohol-consumption behaviour and genetic variants were analysed with a likelihood ratio test, wherein a multiplicative interaction term was added to a logistic regression model. There was an independent association between the C677T polymorphism and thyroid cancer risk but not for drinking history. For C677T C/C homozygotes, individuals with a history of alcohol consumption showed a protective OR (95% CI) of 0.42 (0.15–1.13) when never drinkers were used as the reference. However, this protective association was not observed among individuals with a T+ allele with an OR (95% CI) of 1.27 (0.89–1.82), showing different directions for the association between genotypes with a significant interaction (P_interaction = 0.009). Based on the genetic characteristics of individuals included, an interaction between alcohol intake and MTHFR C677T may modify the risk of thyroid cancer.

Serum folate concentration and the incidence of lung cancer

Background

Lung cancer is a leading cause of cancer-related mortality globally. Folate helps to maintain DNA integrity and to regulate gene expression. Serum folate levels may affect the risk of several cancers, including lung cancer. In this study we evaluated the association between serum folate concentration and variations in genes involved in folate metabolism with lung cancer incidence in Poland.

Methods

The study included 366 lung cancer patients and 366 control subjects. We measured serum folate concentration and genotyped six variants in MTHFR, MTR and MTRR genes. The odds ratios of being diagnosed with lung cancer were calculated using conditional univariable and multivariable logistic regression with respect to folate level and genotypes.

Results

The mean serum folate level was lower in lung cancer cases than in control group (20.07 nmol/l vs. 22.52 nmol/l, p = 0.002). The odds ratio for lung cancer declined with increasing serum content of the folate. The folate concentration of >25.71 nmol/l (IVth quartile) in comparison to <15.92 nmol/l (Ist quartile) was associated with an odds ratio of 0.61 (95%CI 0.40–0.95, p = 0.03). The analysis of variations in MTHFR, MTR and MTRR genes did not reveal any significant difference between lung cancer cases and controls in univariable and multivariable analyses.

Conclusion

In this case-control study, lower serum folate concentrations were associated with a higher risk of lung cancer diagnosis. Although previous findings have been somewhat mixed, our results add to the evidence that circulating folate levels may be an indicator of lung cancer risk.

Lack of association between the MTHFRC677T polymorphism and lung cancer in a Turkish population

BACKGROUND

In this case-control study, we aimed to investigate the relationship between the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and lung cancer.

MATERIALS AND METHODS

Total 200 individuals including 100 patients with lung cancer and 100 controls were analyzed. Genotyping of MTHFR C677T was performed using PCR and RFLP methods.

RESULTS

The majority of the patients were men and 90% were smokers. We found that the risk ratio for development of LC was 13-times higher in smokers compared with non-smokers between patient and control groups in our study (OR:13.5, 95%CI:6.27-29.04, p:0.0001). Besides, the risk ratio for development of LC was nine times higher in individuals with cancer history in their family than those without cancer history (OR:9.65, 95%CI: 2.79-33.36; p:0.0001). When genotype distributions and allele frequencies were analyzed in the study groups, no significant difference was apparent (χ2:0.53, p=0.76). In addition, no correlation between genotypes of MTHFRC677T polymorphism and histological type of LC was found (χ2:0.99, p=0.60).

CONCLUSIONS

These results suggest that there was no association between the MTHFR C677T polymorphism and lung cancer in the Turkish population.

Environmental tobacco smoke exposure and lung cancer: A systematic review

AIM: To review evidence relating passive smoking to lung cancer risk in never smokers, considering various major sources of bias.

METHODS: Epidemiological prospective or case-control studies were identified which provide estimates of relative risk (RR) and 95%CI for never smokers for one or more of seven different indices of exposure to environmental tobacco smoke (ETS): The spouse; household; workplace; childhood; travel; social and other; and total. A wide range of study details were entered into a database, and the RRs for each study, including descriptions of the comparisons made, were entered into a linked database. RRs were derived where necessary. Results were entered, where available, for all lung cancer, and for squamous cell cancer and adenocarcinoma. “Most adjusted” results were entered based on results available, adjusted for the greatest number of potential confounding variables. “Least adjusted” results were also entered, with a preference for results adjusted at least for age for prospective studies. A pre-planned series of fixed-effects and random-effects meta-analyses were conducted. Overall analyses and analyses by continent were run for each exposure index, with results for spousal smoking given by sex, and results for childhood exposure given by source of ETS exposure. For spousal exposure, more extensive analyses provide results by various aspects of study design and definition of the RR. For smoking by the husband (or nearest equivalent), additional analyses were carried out both for overall risk, and for risk per 10 cigarettes per day smoked by the husband. These adjusted for uncontrolled confounding by four factors (fruit, vegetable and dietary fat consumption, and education), and corrected for misclassification of smoking status of the wife. For the confounding adjustment, estimates for never smoking women were derived from publications on the relationship of the four factors to both lung cancer risk and at home ETS exposure, and on the correlations between the factors. The bias due to misclassification was calculated on the basis that the proportion of ever smokers denying smoking is 10% in Asian studies and 2.5% elsewhere, and that those who deny smoking have the same risk as those who admit it. This approach, justified in previous work, balances higher true denial rates and lower risk in deniers compared to non-deniers.

RESULTS: One hundred and two studies were identified for inclusion, published in 1981 onwards, 45 in Asia, 31 in North America, 21 in Europe, and five elsewhere. Eighty-five were of case-control design and 17 were prospective. Significant (P < 0.05) associations were noted, with random-effects of (RR = 1.22, 95%CI: 1.14-1.31, n = 93) for smoking by the husband (RR = 1.14, 95%CI: 1.01-1.29, n = 45) for smoking by the wife (RR = 1.22, 95%CI: 1.15-1.30, n = 47) for workplace exposure (RR = 1.15, 95%CI: 1.02-1.29, n = 41) for childhood exposure, and (RR = 1.31, 95%CI: 1.19-1.45, n = 48) for total exposure. No significant association was seen for ETS exposure in travel (RR = 1.34, 95%CI: 0.94-1.93, n = 8) or in social situations (RR = 1.01, 95%CI: 0.82-1.24, n = 15). A significant negative association (RR = 0.78, 95%CI: 0.64-0.94, n = 8) was seen for ETS exposure in childhood, specifically from the parents. Significant associations were also seen for spousal smoking for both squamous cell carcinoma (RR = 1.44, 95%CI: 1.15-1.80, n = 24) and adenocarcinoma (RR = 1.33, 95%CI: 1.17-1.51, n = 30). Results generally showed marked heterogeneity between studies. For smoking by either the husband or wife, where 119 RR estimates gave an overall estimate of (RR = 1.21, 95%CI: 1.14-1.29), the heterogeneity was highly significant (P < 0.001), with evidence that the largest RRs were seen in studies published in 1981-89, in small studies (1-49 cases), and for estimates unadjusted by age. For smoking by the husband, the additional analyses showed that adjustment for the four factors reduced the overall (RR = 1.22, 95%CI: 1.14-1.31) based on 93 estimates to (RR = 1.14, 95%CI: 1.06-1.22), implying bias due to uncontrolled confounding of 7%. Further correction for misclassification reduced the estimate to a marginally non-significant (RR = 1.08, 95%CI: 0.999-1.16). In the fully adjusted and corrected analyses, there was evidence of an increase in Asia (RR = 1.18, 95%CI: 1.07-1.30, n = 44), but not in other regions (RR = 0.96, 95%CI: 0.86-1.07, n = 49). Studies published in the 1980’s, studies providing dose-response data, and studies only providing results unadjusted for age showed elevated RRs, but later published studies, studies not providing dose-response data, and studies adjusting for age did not. The pattern of results for RRs per 10 cigs/d was similar, with no significant association in the adjusted and corrected results (RR = 1.03, 95%CI: 0.994-1.07).

CONCLUSION: Most, if not all, of the ETS/lung cancer association can be explained by confounding adjustment and misclassification correction. Any causal relationship is not convincingly demonstrated.

Folate pathway gene MTHFR C677T polymorphism and risk of lung cancer in Asian populations

BACKGROUND

Previous studies concerning the association between the 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism with lung cancer in Asian populations have provided inconclusive findings.

AIM

A meta-analysis was performed to investigate a more reliable association between MTHFR C677T polymorphism and lung cancer in Asians.

MATERIALS AND METHODS

A comprehensive search was conducted to identify all case-control studies of MTHFR polymorphisms and lung cancer in Asia, using odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of any association.

RESULTS

Meta-analysis results suggested that the MTHFR C677T polymorphism contributed to an increased lung cancer risk in Asian populations (for T vs C: OR=1.11, 95%CI=1.0-1.23; for CT vs CC: OR= 1.1, 95%CI= 0.95-1.2 ; for TT+CT vs CC: OR=1.13, 95%CI=1.0-1.30; for TT vs CC: OR=1.25, 95%CI=1.01-1.30; for TT vs CT+CC: OR=1.16, 95%CI=1.0-1.36).

CONCLUSIONS

MTHFR C677T polymorphism is significantly associated with lung cancer in Asians.

A genome-wide gene-environment interaction analysis for tobacco smoke and lung cancer susceptibility

Tobacco smoke is the major environmental risk factor underlying lung carcinogenesis. However, approximately one-tenth smokers develop lung cancer in their lifetime indicating there is significant individual variation in susceptibility to lung cancer. And, the reasons for this are largely unknown. In particular, the genetic variants discovered in genome-wide association studies (GWAS) account for only a small fraction of the phenotypic variations for lung cancer, and gene-environment interactions are thought to explain the missing fraction of disease heritability. The ability to identify smokers at high risk of developing cancer has substantial preventive implications. Thus, we undertook a gene-smoking interaction analysis in a GWAS of lung cancer in Han Chinese population using a two-phase designed case-control study. In the discovery phase, we evaluated all pair-wise (591 370) gene-smoking interactions in 5408 subjects (2331 cases and 3077 controls) using a logistic regression model with covariate adjustment. In the replication phase, promising interactions were validated in an independent population of 3023 subjects (1534 cases and 1489 controls). We identified interactions between two single nucleotide polymorphisms and smoking. The interaction P values are 6.73 × 10(-) (6) and 3.84 × 10(-) (6) for rs1316298 and rs4589502, respectively, in the combined dataset from the two phases. An antagonistic interaction (rs1316298-smoking) and a synergetic interaction (rs4589502-smoking) were observed. The two interactions identified in our study may help explain some of the missing heritability in lung cancer susceptibility and present strong evidence for further study of these gene-smoking interactions, which are benefit to intensive screening and smoking cessation interventions.

5,10-Methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTRR), and methionine synthase reductase (MTR) gene polymorphisms and adult meningioma risk

The causes of meningiomas are not well understood. Folate metabolism gene polymorphisms have been shown to be associated with various human cancers. It is still controversial and ambiguous between the functional polymorphisms of folate metabolism genes 5,10-methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTRR), and methionine synthase reductase (MTR) and risk of adult meningioma. A population-based case–control study involving 600 meningioma patients (World Health Organization [WHO] Grade I, 391 cases; WHO Grade II, 167 cases; WHO Grade III, 42 cases) and 600 controls was done for the MTHFR C677T and A1298C, MTRR A66G, and MTR A2756G variants in Chinese Han population. The folate metabolism gene polymorphisms were determined by using a polymerase chain reaction–restriction fragment length polymorphism assay. Meningioma cases had a significantly lower frequency of MTHFR 677 TT genotype [odds ratio (OR) = 0.49, 95 % confidence interval (CI) 0.33–0.74; P = 0.001] and T allele (OR = 0.80, 95 % CI 0.67–0.95; P = 0.01) than controls. A significant association between risk of meningioma and MTRR 66 GG (OR = 1.41, 95 % CI 1.02–1.96; P = 0.04) was also observed. When stratifying by the WHO grade of meningioma, no association was found. Our study suggested that MTHFR C677T and MTRR A66G variants may affect the risk of adult meningioma in Chinese Han population.

Polymorphism of cytosolic serine hydroxymethyltransferase and breast cancer risk: evidence from a meta-analysis

One-carbon metabolism has been presumed to influence cancer pathogenesis. Cytosolic serine hydroxymethyltransferase (cSHMT) is a critical enzyme in one-carbon metabolism pathway. Until now, many studies have investigated the association between cSHMT (also named SHMT1) C1420T polymorphism and breast cancer risk. However, the results remained conflicting rather than conclusive. Literature search was conducted using PubMed, Embase, and China National Knowledge Infrastructure (CNKI) databases until December 2013 to identify studies investigating the association of SHMT1 C1420T polymorphism with breast cancer risk. The strength of the association was assessed by the summary odd ratios (ORs) and their corresponding 95 % confidence interval (CI). Seven studies with a total of 5,534 cases and 6,581 controls were included. Overall, no association was detected between SHMT1 C1420T polymorphism and breast cancer risk (T vs. C, OR = 0.97, 95 % CI = 0.92-1.03). In the subgroup analysis based on ethnicity, SHMT1 C1420T polymorphism has shown a protective effect on breast cancer in Asians (T vs. C, OR = 0.78, 95 % CI = 0.66-0.93) but not in Caucasian (T/T vs. C/C, OR = 0.98, 95 % CI = 0.86-1.12). Significant heterogeneity across studies could be observed in some genetic comparison models in the overall estimation (C/T vs. C/C, P het = 0.004; T/T+C/T vs. C/C, P het = 0.006) but turned to be mild in all comparison models when stratified by ethnicity. Our meta-analysis failed to detect association between SHMT1 C1420T polymorphism and breast cancer risk. However, we found evidence for association of SHMT1 C1420T polymorphism with significantly reduced risk of breast cancer in Asians. Further well-designed studies with larger sample size and better selected controls are warranted.

Influence of methylenetetrahydrofolate reductase C677T polymorphism on the risk of lung cancer and the clinical response to platinum-based chemotherapy for advanced non-small cell lung cancer: an updated meta-analysis

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) has been implicated in lung cancer risk and response to platinum-based chemotherapy in advanced non-small cell lung cancer (NSCLC). However, the results are controversial. We performed meta-analysis to investigate the effect of MTHFR C677T polymorphism on lung cancer risk and response to platinum-based chemotherapy in advanced NSCLC.

MATERIALS AND METHODS

The databases of PubMed, Ovid, Wanfang and Chinese Biomedicine were searched for eligible studies. Nineteen studies on MTHFR C677T polymorphism and lung cancer risk and three articles on C677T polymorphism and response to platinum-based chemotherapy in advanced NSCLC, were identified.

RESULTS

The results indicated that the allelic contrast, homozygous contrast and recessive model of the MTHFR C677T polymorphism were associated significantly with increased lung cancer risk. In the subgroup analysis, the C677T polymorphism was significantly correlated with an increased risk of NSCLC, with the exception of the recessive model. The dominant model and the variant T allele showed a significant association with lung cancer susceptibility of ever smokers. Male TT homozygote carriers had a higher susceptibility, but the allelic contrast and homozygote model had a protective effect in females. No relationship was observed for SCLC in any comparison model. In addition, MTHFR 677TT homozygote carriers had a better response to platinum-based chemotherapy in advanced NSCLC in the recessive model.

CONCLUSION

The MTHFR C677T polymorphism might be a genetic marker for lung cancer risk or response to platinum- based chemotherapy in advanced NSCLC. However, our results require further verification.

Serum vitamin B6, folate, and homocysteine concentrations and oxidative DNA damage in Japanese men and women

OBJECTIVE

Higher vitamin B status has been linked to a lower risk for cancer, but the underlying mechanism remains elusive. The aim of the present study was to examine the association of pyridoxal, folate, and homocysteine (Hcy) with urinary 8-hydroxydeoxyguanosine (8-OHdG), a marker of oxidative DNA damage.

METHODS

The participants were 500 employees (293 men and 207 women), ages 21 to 66 y, of two municipal offices in Japan. Serum pyridoxal and Hcy concentrations were measured using high-performance liquid chromatography (HPLC) method, and serum folate concentrations were measured using chemiluminescent immunoassay. Urinary 8-OHdG concentrations were measured using HPLC method. Multiple regression was used to estimate means of 8-OHdG for each tertile of pyridoxal, folate, and Hcy with adjustment for potential confounders.

RESULTS

In multivariate analysis, 8-OHdG concentration was inversely associated with pyridoxal concentration in men (P for trend = 0.045) but not in women. The association in men was confined to non-smokers (P for trend = 0.033) or those who consumed no or < 20 g/d of ethanol (P for trend = 0.048). 8-OHdG concentrations were not appreciably associated with folate and Hcy concentrations.

CONCLUSION

The results suggest that vitamin B6, but not folate and homocysteine, plays a role against oxidative DNA damage in Japanese men.

Meta-analysis on MTHFR polymorphism and lung cancer susceptibility in East Asian populations

Lung cancer is the most frequently occurring type of cancer worldwide and the leading cause of cancer mortality. Environmental and genetic factors play important roles in lung carcinogenesis. The aim of this meta-analysis was to investigate the association between methylenetetrahydrofolate reductase (MTHFR) polymorphism and the risk of lung cancer in East Asian populations. Related articles were identified through searching literature databases, such as PubMed, EMBASE, Web of Science, Chinese Biomedicine and CNKI. The odds ratio (OR) values in those studies were incorporated by meta-analysis to assess lung cancer susceptibility associated with the MTHFR mutation genotype. The MTHFR C677TT genotype exhibited a significantly increased risk of lung cancer compared to the MTHFR 677CC/CT genotype (OR=1.24; 95% CI, 1.01-1.52). No relationship was identified between the other MTHFR C677T genetic models and the risk of lung cancer and there was no significantly increased risk of lung cancer in A1298C genetic models. In a subgroup of hospital-based controls, according to the source of controls, the C677TT genotype exhibited a significantly increased risk of lung cancer, compared to the C677CC genotype (OR=3.01; 95% CI, 1.07-8.46). In the stratified analysis, the study indicated that the MTHFR 677TT genotype was associated with a significant increase in the risk of lung squamous carcinoma (OR=1.53; 95% CI, 1.09-2.14), whereas no association was observed between the MTHFR C677TT genotype and the risk of lung adenocarcinoma. No association was observed between MTHFR C677TT polymorphism and the risk of lung cancer when smoking was considered. In conclusion, the meta-analysis results suggested that MTHFR C677T polymorphisms exhibit a significantly increased risk of lung cancer and that the MTHFR 677TT genotype is associated with a significantly increased risk of lung squamous carcinoma.

Opportunities and challenges for selected emerging technologies in cancer epidemiology: mitochondrial, epigenomic, metabolomic, and telomerase profiling

Remarkable progress has been made in the last decade in new methods for biologic measurements using sophisticated technologies that go beyond the established genome, proteome, and gene expression platforms. These methods and technologies create opportunities to enhance cancer epidemiologic studies. In this article, we describe several emerging technologies and evaluate their potential in epidemiologic studies. We review the background, assays, methods, and challenges and offer examples of the use of mitochondrial DNA and copy number assessments, epigenomic profiling (including methylation, histone modification, miRNAs, and chromatin condensation), metabolite profiling (metabolomics), and telomere measurements. We map the volume of literature referring to each one of these measurement tools and the extent to which efforts have been made at knowledge integration (e.g., systematic reviews and meta-analyses). We also clarify strengths and weaknesses of the existing platforms and the range of type of samples that can be tested with each of them. These measurement tools can be used in identifying at-risk populations and providing novel markers of survival and treatment response. Rigorous analytic and validation standards, transparent availability of massive data, and integration in large-scale evidence are essential in fulfilling the potential of these technologies.

Methylenetetrahydrofolate reductase 677TT genotype might be associated with an increased lung cancer risk in Asians

BACKGROUND

The association between methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism and lung cancer risk has been studied in various populations with conflicting results. The aim of this study was to assess the association strength by a meta-analysis of published studies.

METHODS

We searched PubMed and Chinese Biomedical (CBM) databases for relevant literatures published by July 18, 2012. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated to assess the strength of the association.

RESULTS

A total of 20 studies comprising 11,653 cases and 12,032 controls were included in the final meta-analysis. Using the random effect model, we found that MTHFR 677TT variant genotype was associated with an increased lung cancer risk (OR=1.26, 95% CI=1.05-1.50, P=0.011 for TT vs. CC; OR=1.19, 95% CI=1.03-1.37, P<0.001 for TT vs. CC+CT; OR=1.11, 95% CI=1.02-1.22, P=0.017 for T allele vs. C allele). In the further stratified analyses, the increased lung cancer risk was found in Asian subjects (OR=1.31, 95% CI=1.01-1.71, P=0.045 for TT vs. CC; OR=1.17, 95% CI=1.00-1.38, P=0.048 for TT vs. CC+CT). There were no evidences for obvious publication bias in the overall meta-analysis and Asian subjects.

CONCLUSIONS

MTHFR 677TT genotype might increase the susceptibility of lung cancer, especially in Asians.

A literature review of MTHFR (C677T and A1298C polymorphisms) and cancer risk

5,10-Methlenetetrahydrofolate reductase (MTHFR) is one of the most important enzymes for folate metabolism. This enzyme is mapped on chromosome 1, which is located at the end of the short arm (1p36.3). The C677T and A1298C are MTHFR polymorphisms that decrease in vitro MTHFR enzyme activity. Folate metabolism plays a key role in cell metabolism. These reactions are associated with purine-pyrimidine synthesis: DNA, RNA, and protein methylation. Polymorphism is also a factor in biodiversity, and be affected by ethnic heritage and geographic locale. In the case of unknown outcomes, not only should all geographical regions be investigated to ascertain biodiversity, but all populations as well to fully understand the variations in the effect. PUBMED was searched from January 2006 to December 2011 to develop an investigatory pursuit strategy. MTHFR, cancer, C677T, A1298C, and polymorphisms were key words used to focus the search. The literature review included all published relevant cancer types and MTHFR polymorphisms for that 5 years period. All selected polymorphisms data for cancer types was listed in tables for easy access and retrieval.